It* Dry-Rot of 
Incense Cedar 



By J. S BOYCE 




Sf Dissertation Presented to the 
LeJana Stanford, Jr., University for 
the Degree of Doctor of Philosophy 



UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 871 

Contribution from the Bureau of Plant Industry 
WM. A. TAYLOR, Chief 



Washington, D. C. 



PROFESSIONAL PAPER 



November 10, 1920 



THE DRY-ROT OF INCENSE CEDAR 

By 

J. S. BOYCE, Assistant Pathologist 
Office of Investigations in Forest Pathology 



CONTENTS 



Importance of Incense Cedar .... 1 

Total-Loss Factors 2 

Method of Collecting Data 4 

Secondary Rots 7 

The Dry-Rot 8 



Page 
Application of Results ........ 49 

Relative Importance of Dry-Rot . . 49 

Control of Dry-Rot 49 

Summary 55 

Literature Cited 57 




WASHINGTON 
GOVERNMENT PRINTING OFFICE 

1920 






Gift 



UNITED STATES DEPARTMENT OF AGRICULTURE 




BULLETIN No. 871 



Contribution from the Bureau of Plant Industry 
WM. A. TAYLOR, Chief 




J^P^Lft. 



Washington, D. C. 



PROFESSIONAL PAPER 



November 10, 1920 



THE DRY-ROT OF INCENSE CEDAR. 

By J. S. Boyce, Assistant Pathologist, Office of Investigations in Forest Pathology. 



CONTENTS. 



Page. 

Importance of incense cedar 1 

Total-loss factors 2 

Method of collecting data 4 

Secondary rots 7 

The dry-rot 8 



Page. 

Application of results 49 

Relative importance of dry-rot 49 

Control of dry-rot 49 

Summary 55 

Literature cited 57 



IMPORTANCE OF INCENSE CEDAR. 

Incense cedar (Libocedrus decurrens) is of considerable economic 
importance on the Pacific coast. The available supply of this species, 
which never occurs alone but always in mixture, chiefly with yellow 
pine, Jeffrey pine, sugar pine, Douglas fir, and white fir, averaging 
about 8 per cent of the stand, although often forming as high as 30 
to 50 per cent, is estimated at 11 billion feet, 10 billion of which 
occurs in California (17, pp. 9-10). * That the wood is very valuable 
for special purposes on account of certain qualities has been clearly 
pointed out by Mitchell (17, pp. 2-9) recently and was mentioned by 
Von Schrenk (26, p. 69) 20 years ago. However, in spite of the well- 
known value of the wood, only about 30 million feet is cut annually 
in California. The stunipage rate is low and the price for the finished 
product often little more than pays the cost of logging and manufac- 
ture, according to Mitchell (17, p. 6). 

The reason for this is obvious. The heartwood of incense cedar is 
commonly rendered totally worthless by the so-called dry-rot caused 
by Polyporus amarus. An idea of the quantity of timber rendered 
unmerchantable by this dry-rot may be obtained from Mitchell's 
statement (17, p. 3) that so common is this defect that it is the usual 
practice to cut estimates of this species from 30 to 50 per cent on ac- 



1 The serial numbers in parentheses refer to " Literature cited " at the end of the bulletin. 
182803°— 20— Bull. 871 1 



2 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 

count of it. This leads to a distinct prejudice against the species 
on the part of both the lumberman and the forester. The lumber- 
man is naturally averse to handling a large quantity of practically 
worthless material for which there is little or no market in order to 
secure a small amount of valuable material, when the profit on the 
more valuable product is not sufficient to carry adequately the entire 
product. The forester sees a species of very little value, as attested 
by the low stumpage rate, occupying space which might be given 
over to surrounding species on which a much higher stumpage rate 
could be realized. 

This prejudice, which has resulted in the classification of incense 
cedar as an "inferior" species, is not based on any inherent quality 
of the tree itself, for sound cedar wood, as has already been stated, 
is quite valuable, finding a ready market; and the tree, on account of 
its relatively high tolerance of shade, particularly during its earlier 
life, is a valuable component of the mixed stand in which it occurs. 

Incense cedar is a thrifty, aggressive species, quite tolerant of shade, 
and has a definite, permanent place in the forests of the Pacific coast. 
Its aggressiveness makes it almost an impossibility to eradicate the 
species entirely, and such an attempt would be highly inadvisable 
and might result in unforeseen disastrous consequences resulting 
from an artificial change in the composition of the stand. Greeley 
(6, p. 112) and Meinecke (16, pp. 21-22) have specifically advised 
against this. The lumberman, logging in types with incense cedar 
represented, faces the necessity of handling a large quantity of almost 
worthless timber, which if sound would be of high value. 

Since incense cedar probably can not be eliminated from the stand, 
the problem presents itself of the proper treatment of an inferior 
species which in time will undoubtedly become quite valuable. 
Foresters and lumbermen are showing more and more interest in the 
question, fully realizing that this species will always have to be 
reckoned with. We must have exact, far-reaching studies not only 
to handle properly and utilize the cedar at present, but to lay the foun- 
dations for a rational system of silvicultural management for the 
future. Production is inevitable; proper treatment must be evolved. 
Consequently, the study on which this paper is based was under- 
taken in an attempt to throw light on certain of the phases involved. 

TOTAL-LOSS FACTORS. 

Throughout American forestry literature dealing with regulation 
and management are found statements in regard to individual com- 
ponents of mixed stands to the effect that "in virgin forests incre- 
ment equals decay," or sometimes "deterioration" is used in place 
of "decay." Chapman (2, p. 317) and Meinecke (16, p. 3-4) have 
shown this generalization to be of absolutely no value, since the as- 



DRY-ROT OF INCENSE CEDAR. 8 

sumption is based on the factors of increment and decay, of which 
almost nothing is known. When deterioration is used in place of 
decay, it is an impossibility to reach a conclusion as to just what 
factors of loss are included in the term. 

The term " total loss" has been introduced byMeinecke (16, p. 4-5) 
to cover all factors which lead to any reduction of increment or 
actual volume in a stand, and he makes a strong plea for exact studies 
of all components of the total-loss factor for individual species before 
any effort is made to determine this for the mixed stand. 

To determine the components of the total-loss factor for any given 
species is merely a matter of simple observation, but to gauge accu- 
rately their relative importance is not easy, calling for careful com- 
prehensive work. 

In the case of incense cedar the numerical dropping out of indi- 
vidual trees, the mechanical injuries caused by fire, frost, light- 
ning, the breaking of branches, and other causes, a mistletoe, and 
several fungi play a more or less important part in the total-loss 
factor. These components may be divided into two broad classes, 
those reducing the future capital of timber (lessening the increment) 
and those reducing the present capital of timber (destroying actual 
merchantable material). It is impossible to draw a sharp line 
between these two classes, since some components find a place in 
both. 

The unavoidable yearly dropping out of certain trees, varying in 
size from seedlings to veterans, affects both the increment and mer- 
chantable material in a stand. Mechanical injuries, while primarily 
causing a loss in the merchantable timber, to some extent interfere 
with the normal growth of the tree, thus reducing the increment. 

A mistletoe (Phoradendron juniperinum libocedri), the incense-cedar 
rust (Gymnosporangium blasdaleanum) (15, p. 35-37; 11), a leaf-in- 
habiting fungus (Stigmatea sequoiae) (3, p. 87; 4, p. 314), and the black 
cobweb fungus (Herpotrichia nigra) all primarily cause a loss in the 
future capital of timber by reducing the annual increment of infected 
trees. The amount of this loss is exceedingly difficult to gauge 
accurately, but it is so small in relation to the damage caused by 
the agencies reducing the present capital of timber that the above- 
mentioned organisms are given no consideration in this paper except 
incidental mention. Under certain conditions, the mistletoe is 
responsible for a slight reduction in the merchantable contents of 
the host tree by causing spindle to barrel shaped swellings on the 
boles of mature and overmature trees (14, p. 37). The wood of 
these swellings is rendered valueless for lumber, owing to the pres- 
ence of the mistletoe "sinkers," or roots, either living or dead. 
Swellings are rarely, if ever, found on the boles of younger trees. 



4 BULLETIN 811, U. S. DEPARTMENT OF AGRICULTURE. 

Most important of all, however, is the loss of the present capital 
of timber through decay. The organisms causing decay in incense 
cedar are the pouch fungus (Polyporus volvatus) , Polystictus abietinus, 
Polystictus versicolor, Lenzites sepiaria, the red-belt Fomes {Forties 
pinicola), some unknown fungi, and the incense-cedar dry-rot fungus 
(Polyporus amarus). The first five listed have never been found 
attacking living incense cedars. There are several forms of decay 
of trifling importance in living trees, the causes of which have not 
been determined. Polyporus schweinitzii has been found in one case. 

Standing out above all the other components of the total-loss 
factor is Polyporus amarus, causing dry-rot in the heartwood of the 
tree. Since the first utilization of incense cedar, the great destruc- 
tion wrought by this fungus has been a matter of extreme concern 
to lumbermen and foresters, as is shown by the constant references 
to the decay found throughout the literature wherever incense cedar 
is mentioned. 

The importance of dry-rot can not be overestimated, and it is on 
this point, together with the related mechanical injuries, that a study 
of the total-loss factor must be concentrated; the other considera- 
tions play a distinctly secondary role. 

METHOD OF COLLECTING DATA. 

SELECTION OF AREAS. 

The first step in carrying on a study of the total-loss factors in 
any given species is the selection of proper areas for work. The 
areas selected, if the results are to serve for any but strictly local 
application, must be representative of the larger unit or region of 
which they form a part. It is self-evident then that areas located 
in the altitudinal or horizontal extremes of the range of the species 
under investigation must be avoided. The results of a study on 
such areas, while scientifically interesting, would be absolutely with- 
out practical value, since they would only answer for a limited unit 
on which the stand is abnormal and would fail to answer any ques- 
tions in regard to the major and more valuable portion of the range 
of the species. 

All indications tend to show that there is a considerable variation 
in the growth and development of incense cedar in different parts 
of its range. This has already been hinted at by Mitchell (17, p. 9, 
13, 23, 24). The writer distinguishes three distinct ranges based 
on the development of the tree, and these are termed, for conve- 
nience, the optimum, intermediate, and extreme ranges. 

The best development is found in the southern Sierras, particularly 
on the Sierra, Sequoia, and Stanislaus National Forests, and the 
southern portion of the Eldorado National Forest, where the species 
is relatively rapid growing and thrifty. 



DRY-ROT OF INCENSE CEDAR. 

In the intermediate range, comprising the northern Sierras and 
the Coast Ranges, slower growth is the rule, and in the mixed stand 
where the cedar always occurs it plays a distinctly secondary part 
and might almost be classed as an understory tree. 

The poorest development is found in the extreme range, which 
includes stands at the horizontal and altitudinal extremes of the dis- 
tribution of the species. In such situations the trees are short, 
scrubby, and relatively of little value. 

With the above facts in mind, it was considered essential to choose 
areas representative of the intermediate and optimum range; the 
extreme range could be neglected, since it is of no practical im- 
portance. 

In the uneven-aged stands care had to be observed to select areas 
on which all age classes were represented, since if there is a relation 
between any of the total-loss factors and age of the tree, this would 
fail to appear if even-aged or nearly even-aged trees alone were con- 
sidered. 

Observation and a preliminary study by Meinecke 1 showed con- 
clusively that the total-loss factor of supreme importance in the 
case of incense cedar is dry-rot caused by Polyporus amarus. Above 
all, then, it was essential to select stands in which dry-rot was com- 
mon, using discretion not to make the selections where loss from 
dry-rot was far above or below normal. Other total-loss factors, 
particularly mechanical injuries, could not be disregarded and were 
carefully considered. 

With a knowledge of the habits and condition of incense cedar 
throughout its range, several possible areas were tentatively chosen, 
a careful examination made in each case, and then the most suitable 
stands were decided upon. 

DESCRIPTION OF AREAS. 

The area selected to represent the intermediate range is at Sloat, 
Calif., within the boundaries of the Plumas National Forest, in the 
northern Sierra Nevada Mountains. In general, the region is one of 
heavy snowfall, with moderate winter temperatures and a long, 
dry, warm summer season. Lightning storms are not very frequent. 

The tract has a relative altitude of 4,300 to 4,700 feet. The fairly 
deep soil is a decomposed lava, normally dry and loose. 

The virgin mieven-aged stand, with a strong representation of 
mature and badly overmature trees of all species, is principally 
composed of western yellow pine {Pinus ponderosa), Jeffrey pine 
{Pinus jeffreyi), and Douglas fir (Pseudotsuga taxifolia). Where 

1 The writer wishes to acknowledge his indebtedness to Dr. E . P. Meinecke, who first inaugurated a study 
of incense cedar in 1912, the data obtained being included in this paper, for advice and direction through- 
out the course of all the later work. The essential methods followed in this study are outlined by him in 
United States Department of Agriculture Bulletin 275 (16). 



6 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 

Douglas fir predominates, the two pines take second place, and vice 
versa. Third in order comes incense cedar, while sugar pine (Pinus 
larnbertiana) and white fir (Abies concolor) are but lightly represented. 

In the more dense stand on the lower slopes and in the draws 
incense cedar forms a distinct understory, overtopped by all the other 
species; it is in such localities that the cedar shows every indication 
of slow growth and strong suppression. On the higher slopes and 
along the ridges, where the stand is more open, the cedar in individual 
cases often assumes a better position in the stand, and all the trees of 
this species, with few exceptions, appear to be more thrifty and to 
have made a more rapid growth. Badly suppressed trees are rare. 

The three areas selected to represent the optimum range are on 
the Stanislaus National Forest in the southern Sierra Nevada Moun- 
tains. One of these is at Strawberry, at an altitude of 5,300 to 5,600 
feet; a second at Cow Creek, about 5 miles north and east of the 
first and at about the same elevation; and the third at Crockers 
Station, about 30 miles to the south and a little east of the Straw- 
berry area and at an altitude of about 4,500 feet. Since the areas 
are so nearly alike, a composite description will suffice. 

The soil is a rather deep, loose, decomposed granite, with many 
large granite bowlders. It is normally somewhat dry. 

The virgin uneven-aged overmature stand is rather open and is 
composed of sugar pine, western yellow pine, Jeffrey pine, white fir, 
incense cedar, and Douglas fir. Normally the pines predominate, 
with white fir or incense cedar next in order, Douglas fir being found 
sparingly only on the Crocker area. Incense cedar is represented 
by trees of all ages, and on the whole appears very thrifty. There 
are many individuals of large size, comparatively young. The cedar 
here is far from forming such a distinct understory as on the Sloat 
area, so the stand has made a much more rapid growth. 

NOTES ON INDIVIDUAL TREES. 

After the general notes were completed on an area, work was 
commenced on individual trees. Trees of all ages and conditions 
must be cut for a study of this kind, the primary purpose being to 
determine the age of the stand at which dry-rot becomes extensive. 
Observations on logging operations and the results of Meinecke's 
preliminary study had shown that trees between 100 and 240 years 
old would yield the essential data on this point, and it was within 
these age limits that the investigation was concentrated, but the 
lower and higher ages were not neglected by any means. This 
resulted in clear cutting within the ages mentioned, except that those 
trees in which it was plainly apparent an accurate age count could 
not be made were left standing, while only a portion of the trees in 
the stand above and below these ages were cut. Thus, since a given 



DRY-ROT OF INCENSE CEDAR. 7 

tract was not clear cut, the representation of age, diameter breast 
high, and height classes obtained from the study must not be assumed 
as an exact expression of the actual conditions. 

Each tree was cut as closely as possible to a stump height of 18 
inches, then limbed and bucked. The first or butt log was made 
7 feet long and the others 14 feet long, the number of cuts depending, 
of course, on the length of the tree. The last cut was always made 
well in the top near the upper limit of the heartwood. The reason 
for bucking in 7 and 14 foot lengths was purely a practical one; any 
sound heartwood could then be utilized for 7-foot posts. The age 
count at stump height was taken as the age of the tree instead of 
adding a few years corresponding to the height of the stump, since 
the aim is to have all figures taken directly comparable. In this 
case with a minute constant variation no error can be introduced. 
Trees with wounds which destroy the center at stump height were 
avoided when possible, since in such cases an accurate age count 
could not be obtained; hence, trees of this kind are valueless for all 
further calculations in which the exact age is a factor. The sap width 
was obtained from an average of six or eight measurements. Three 
radii were measured to secure the average diameter. Separate 
measurements were made for the area covered by decay. The dates 
of occurrence and closure, when healed, were determined for all 
wounds present. Each log was split at least once in order to reveal 
completely all decay and internal wounds. Great care had to be 
observed in splitting the logs in order to be certain not to miss any 
decay, since the dry-rot occurs in pockets which may be separated 
in a linear direction by several feet of sound wood. This habit of 
"jumping" also made it exceedingly difficult to trace the entrance 
of the decay in certain cases where the decay might be several feet 
removed from any possible point of entrance. It often became 
necessary to split log after log into many small pieces. 

In all, 1,075 trees were analyzed, 509 at Sloat, 266 at Strawberry, 
100 at Cow Creek, and 200 at Crockers Station. 

In all future references in this paper, for the sake of convenience 
the term "intermediate area" will be used to designate the area at 
Sloat, since i^ represents conditions in the intermediate range, and 
the term "optimum area" to designate the combined areas at Straw- 
berry, Cow Creek, and Crockers Station, since they represent condi- 
tions in the optimum range. The results of the field work follow. 

SECONDARY ROTS. 

Under this heading are grouped all decays the causes of which 
are unknown. Such decays are of various types and are almost 
invariably found immediately adjacent to open or healed-over 
wounds, particularly fire scars. Instances were encountered where 



8 BULLETIN 871, IT. S. DEPARTMENT OF AGRICULTURE. 

the decays were so badly eaten out by insects as to preclude any 
description of the rot. By reason of this, some light infections of 
Polyporus amarus may have been included under secondary rots, 
but such cases have undoubtedly been very rare. 

Of the 59 infections of second ary rots examined, only 9 resulted 
in culls of any importance, the highest percentage of unmerchant- 
able timber in relation to the total volume of the tree being 19.5 
per cent. In all the remaining 50 trees the infections were negligible. 
These figures show secondary rots to be of only trivial importance in 
reducing the merchantable volume; hence, such decays are not 
further considered in this paper. 

THE DRY-ROT. 

The dry-rot of incense cedar, termed by eastern workers "pecki- 
ness" or "pin-rot," caused by the fungus Polyporus amarus Hedge, 
was first described and figured by Harkness (7) but no cause was 
given. Next Von Schrenk (26, 67-77, pi. 2, 4, 5) described and 
figured the disease without stating the cause, and later (28) he 
mentions Polyporus libocedris, but without giving a description of 
type specimens. Hedgcock (10) first definitely assigned the cause 
of the dry-rot to Polyporus amarus sp. nov. and described the fungus. 
Later Meinecke (15, p. 35-37) presented a brief description of the 
sporophore, accompanied by a photograph of a typical fully devel- 
oped bell-shaped specimen, with the upper surface partially destroyed 
by insects. Murrill (24, p. 25) places the fungus in the genus Fomes. 

Harkness and Moore, Mayr, and Sargent have attributed the cause 
of the dry-rot to Daedalea vorax Hke., but Von Schrenk (26, p. 67-68) 
has shown this to be an error. Farlow and Seymour (5, p. 169) and 
Bryant (1, p. 15) have made the same mistake. 

The dry-rot is very widely distributed. It has been found at 
elevations varying from 650 to 6,480 feet as far north as Oakridge, 
Lane County, Oreg., west to the west of China Flat, Humboldt 
County, Calif., east to Shaver, Fresno County, Calif., and south to 
the north and east of Mentone, San Bernardino County, Calif. In 
fact, from all indications and hearsay evidence it is quite reasonable 
to presume that dry-rot is more or less prevalent in incense . cedar 
throughout the range of the host (30, p. 150-152). 

THE SPOROPHORE. 

Since Hedgcock's description was published, so many sporophores 
have been collected that the original description may be supplemented 
by the following, which is based on the examination of 25 sporophores, 
both fresh and old : 

Polyporus amarus. — Pileus soft and mushy when young, then rather tough and 
cheesy, finally becoming hard and chalky when old, ungulate, bell shaped or occa- 



Bui. 871 , U. S. Dept. of Agriculture. 



Plate I, 




A Fresh Sporophore of Polyporus amarus on a Down Tree. 

Photographed by Gravatt. 



Bui. 871 , U. S. Dept. of Agriculture. 



Plate 1 1 . 





An Old Shot-Hole Cup. The Original Sporophore Issued from the 
Knot Hole at the Top. 

Photographed by Meinecke. 



DRY-ROT OF INCENSE CEDAR. 



9 



sionally subapplanate, often spuriously stipitate from knot holes, 4 to 15 by 5 to 22 
by 5 to 20 cm., commonly 7 to 10 by 11 to 13 by 8 to 13 cm., occasionally abortive 
without hymenial layer, then assuming irregular shapes; surface pubescent when young, 
rimose and chalky when old, at first buff, then tan, and often blotched with brown 
when attacked by insects; margin obtuse, frequently having an outer band of darker 
brown, often slightly furrowed; context homogeneous, 1 lemon-yellow, later buff to 
tan, usually darker near the surface when old, slightly bitter to the taste, 4 to 14 cm. 
thick, commonly 9 to 11 cm., usually friable when dry but occasionally becoming 
partially horny, hard; tubes not stratified, lemon-yellow within, cylindric 0.2 to 3 
cm. in length, shorter next the margin, mouths circular or slightly irregular, 1 to 3 
to a millimeter, lemon or sulphur yellow during growth, turning brown when bruised 
or old, becoming lacerate; under surface of the hymenial layer sometimes exuding 
clear yellow drops of liquid, sweetish to taste; spores hyaline or slightly tinged with 
yellowish brown, smooth, ovoid (200) range 3 to 6.5 p by 4.5 to 9 /x; standard size 
3.5 to 4.5 n by 6.5 to 7 ju, nucleated; cystidia none. 

The following table presents detailed measurements of 24 sporo- 
phores of Polyporus amarus: 

Table I. — Sporophore measurements of the incense-cedar dry-rot fungus. 



cm. cm. cm. 


cm. cm. cm. 


cm. cm. cm. 


3. 8 by 4. 8 by 8.3 


8. by 13. bv 13. 


9. 5 by 17.0 by 13. 3 


4. 2 by 5. 5 by 5.5 


9.0 by 11. 5 by 9.9 


9. 8 by 13. 2 by 13. 


6.0 by 7. 3 by 8.6 


9.0 by 10.0 by 10.0 


10. 3 by 14. 9 by 14. 8 


6. 8 by 11. 2 bv 12. 3 


9.0 by 10. 5 by 11. 


11. 4 by 20. 7 by 19. 8 


7. 5 by 11. 4 bv 9.0 


9. by 13. 3 by 12. 


12. by 16. 4 bv 10. 8 


7. 5 by 17.0 by 8.1 


9.1 by 10. 7 by 8.5 


12. 1 by 21. 2 by 12. 5 


7. 6 by 11. 4 by 9.5 


9.1bvl2.4by 8.9 


14. 5 by 22. by 13. 


8. by 12. 5 by 10. 


9. 5 by 14. 7 by 11.0 


14. 8 by 12. 7 by 16. 5 



The sporophores, which last for one season only even at best, are 
not at all common, a statement which is supported by the number 
of years the dry-rot was known before the cause was definitely 
determined. During certain years sporophores seem to be very 
rare. They most commonly occur in the summer, and especially 
in the fall, but occasionally are found at other seasons. Observa- 
tions record two fresh ones in March in a rather mild climate at an 
altitude of about 3,000 feet in the Sierra Nevada. Another was 
found in a different locality in June. No sporophores have been 
found developing later than October, but occasional fresh ones 
may be carried over from a previous fall into the winter in a frozen 
condition. They are then destroyed in the spring. 

Typically the sporophores are produced on living trees but are, 
on occasions, found on dead fallen trees. (PL I.) Seven such cases 
have been observed during the past five years. In five of these it 
was possible to determine the time which elapsed between the felling 
of the tree and the appearance of the sporophore. Three of the 
sporophores were produced 3 years, one 4 years, and one 27 years 
after the trees had been cut. As to how long the mycelium may 

1 The substance of the sporophore not including the outer layers. 
182803°— 20— Bull. 871 2 



12 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 

always indicate that there is well-developed dry-rot in the heartwood. 
In such infections it is generally possible to distinguish three stages in 
the affected heartwood, with upper and lower limits. These stages 
for convenience are termed total extent, unmerchantable extent, and 
maximum concentration. "Total extent" is expressed by giving 
the height in feet in relation to the ground level of the lowest and 
highest point in the bole of the tree invaded by the fungus without 
regard to radial extent. By "unmerchantable extent" is meant the 
portion of the bole rendered valueless for lumber by the dry-rot, 
while "maximum concentration" covers that portion of the bole in 
which the decay seems to be at its worst. The upper and lower limits 
of all three of these stages may at times coincide, but especially 
that of the unmerchantable extent and maximum concentration. It 
is self-evident that these last two mentioned can never exceed the 
total extent. 

The sporophores and shot-hole cups invariably appeared between 
the upper and lower limits of the maximum concentration. The 
lower limits varied from 3 to 25 feet below the sporophores or shot- 
hole cups, and the upper limits from 4 to 45 feet above them. In every 
case except one the lower limit of the unmerchantable extent was at 0. 
In other words the bole of every tree was unmerchantable, at least 
from the ground level to the sporophore or shot-hole cup. In the one 
exception the unmerchantable extent did not commence until 8.2 
feet from the ground level. This was due to the presence of a large 
open fire scar extending from to 10.8 feet. The fungus distinctly 
avoids the dried-out wood around open wounds, which habit will be 
fully discussed later in this paper. The upper limits of the unmerchant- 
able extent were variable. In the two abortive sporophores the un- 
merchantable portion extended for 10 and 24 feet, respectively, 
above the sporophores, while the extent above the shot-hole cups was 
23 and 53 feet. 

The total extent in every tree with sporophores except one (see 
above, under unmerchantable extent) reached from the sporophore or 
shot-hole cup to the ground level, but the upper extent was variable, 
being for the two sporophores 24 and 25 feet, respectively, and for the 
shot-hole cups ranging from 24 to 53 feet. 

From the figures available it is impossible to make an exact state- 
ment as to the range of the total extent, unmerchantable extent, and 
maximum concentration of the dry-rot in trees with sporophores or 
shot-hole cups, except that it may be safely assumed not only from 
the figures at hand but from observations on logging areas that the 
bole of a tree will always be unmerchantable from the ground level 
to a variable height above a sporophore or shot-hole cup. But it 
must be remembered that an old shot-hole cup indicates a greater 
development for the fungus plant in the tree than does the first 



DRY-ROT OF INCENSE CEDAR. 13 

appearance of a sporophore or fresh shot-hole cup, and one should 
be influenced accordingly in judging the condition of a standing tree. 

THE DECAY. 

The dry-rot, described and pictured by Harkness (7), Von Schrenk 
(26, p. 68, pi. 2), and Meinecke (15, p. 46, pi. 12), is a very characteris- 
tic decay, most closely resembling the so-called peckiness of the 
eastern cypress (Taxodium distichum). Von Schrenk (26, p. 52-53) 
points to this analogy, even suggesting that the two diseases may be 
caused by the same fungus, but tong (12) has disproved this theory. 
The former investigator (29, p. 30) also calls attention to the macro- 
scopical similarity between this dry-rot and the brown-rot of redwood. 

Typically, the decay consists of vertically elongated pockets, 
varying in length from one-half inch to about a foot, which are filled 
with a brown friable mass, and the line of demarcation between the 
sound and decayed wood is very sharp. In some of these pockets 
small cobweblike or feltlike masses of white mycelium occur. The 
pockets are separated from each other by what appears to be sound 
wood, although in some cases streaks of straw-colored or brownish 
wood may extend vertically between two pockets. This is especially 
noticeable between young pockets. When immature the decay is 
faintly yellowish brown, soft and somewhat moist, and not broken 
up in the pockets. At times the mature pockets may be several feet 
long and rather broad; this type always occurs in connection with 
healed-over wounds, particularly healed fire scars in the butt of the 
tree. The decay has never been found in living sapwood and is 
usually confined to the heartwood of the trunk, but in very badly 
decayed trees the dry-rot sometimes extends into the heartwood of 
the larger limbs. 

In the aggregate, the immature decay or advance rot extends but 
a short distance vertically in advance of the typical decay, and a dis- 
tance of 2 feet beyond the last visible evidence of decay to the average 
eye will usually exclude all immature decay. This immature decay 
is very difficult to detect, occurring as it does in pockets, with the 
color in the very earliest stages differing but slightly, if at all, from 
the normal wood. 

An occasional pocket may occur several feet in advance of the main 
body of decay, and while the wood of the pocket itself is of course 
greatly weakened, the intervening wood is probably very little 
affected, since the fungus hyphae are very sparingly found between 
pockets of decay. In all, 566 trees containing typical dry-rot were 
dissected. 

Typical dry-rot with small masses of white mycelium in some of 
the pockets is shown in Plate III. 



16 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 

certain time produce conditions unfavorable for their further develop- 
ment and are forced to seek another field. 

In the wood the hyphge are hyaline, varying in diameter from 
0.8 to 3.3 n but being most commonly 0.8 to 1.7 n, branching and 
rebranching into the finest threads, anastomosing, sparsely septate, 
rarely constricted at the septa, and sometimes having clamp connec- 
tions. They never become so abundant as to fill the tracheids 
completely. Usually the hyphae pass from the lumen of one tracheid 
into that of an adjoining tracheid and then extend up or down 
the lumen, but occasionally a single hypha may cross several 
tracheids in a radial or tangential direction without extending up or 
down their lumens or giving off any branches. The holes in the 
walls of the tracheids made by the hyphse are very small, particularly 
so since the hyphae are often sharply constricted when passing through 
the walls-. Rarely the hyphse are irregular in shape. 

The hyphse composing the cobweblike and feltlike masses of 
mycelium in the badly decayed wood (see p. 13) are usually 
hyaline, but sometimes have granular contents. They vary in diam- 
eter from 0.8 to 40 n, are richly branched, more commonly septate 
than the hypha} found in the wood cells, and sometimes constricted 
at the septa. No clamp connections were found. They frequently 
anastomose. They were often very irregular in shape, and globose 
or spindle-shaped swellings were frequent. 

OTHER FORMS OF DECAY. 

Besides the typical decay alread} T described, two other very 
characteristic forms were found. One of these is characterized by 
small spots or pockets of brown decayed wood varying in width from 
0.5 to 2 mm. (0.02 to 0.08 inch) and in length from 1 to 4 mm. 
(0.04 to 0.16 inch), with the long axis running vertically in the wood. 
In some cases larger decayed spots are formed by the joining of two 
or more smaller ones. The tiny decayed spots are separated by 
apparently sound wood. As for the structure of the decayed wood 
and its reactions with various reagents, these agree exactly with the 
typical form of dry-rot (see p. 14), and this decay is very probably 
an abnormal form of the typical decay caused by Polyporus amarus. 

The other form of decay consists of very small white spots (measure- 
ments as given above) in which the wood has been reduced to cellulose, 
separated by apparently sound wood. The structure of the decayed 
wood is practically as described by Hartig (8, p. 53-54; 9, p. 36-37) 
for decay caused by the ring-scale fungus (Trametes pini), and the rot 
under consideration is undoubtedly caused by this fungus, since, 
through the courtesy of Dr. James K. Weir, the writer has been 
privileged to examine sporophores of Trametes pini with the typical 



iul. 871 , U. S. Dept. of Agriculture. 



Plate III. 




Typical Dry-Rot in Incense Cedar Caused by Polyporus amarus. 

Photographed by Meinecke. 



DRY-KOT OF INCENSE CEDAE. 17 

decay collected on incense cedar in Oregon. As far as the writer can 
ascertain, this is the only collection of its kind now known. Neither 
of these two decays affects the living sapwood. 

The mycelium of both is the same and differs from the mycelium 
of typical dry-rot. Studies were made where these two decays were 
distinct, where they graded into one another, and where they graded 
into the typical dry-rot. The hyphse vary from hyaline to dark 
brown in color, with a diameter ranging from 0.8 to 6.7 fj. but most 
commonly 3 n. The heavier brown hyphse often branch profusely, 
the branches becoming smaller and lighter in color. The smallest 
ones are usually hyaline, and so are some of the larger hyphse. In 
some instances the smaller hyphse are merely continuations of the 
heavier strands. The hyphse are sparsely septate, often constricted 
at the septa and without clamp connections. They bore through the 
cell walls in all directions, but seemingly more often through the 
tangential walls. No p reference is shown for the bordered pits. They 
are characteristically sharply constricted when passing through the 
walls of the tracheids and have marked attachment organs. The 
hyphse did not enlarge in the secondary lamella? when boring through 
the wall, as is shown by Hartig (8, 9) for Trametes pini. Quite typi- 
cally, a single strand may pass tangentially through as many as 20 
or 30 tracheids, often completely traversing an annual ring, without 
sending any side branches into the lumens. This mycelium appears 
to agree closely with that described and figured by Von Schrenk 
(26, pp. 73-74, pis. 4-5), but which he assumed to be secondary and 
in no way connected with the dry-rot. Often the hyphse seem to 
pierce a cell wall without developing in the lumen of the tracheid 
entered, a condition recorded by Hartig (8, p. 46) for Trametes pini. 
However, in so many cases unattached fragments of hyphse were 
found in tracheids through the walls of which the nyphse had pene- 
trated without developing in the lumen that most probably the hyphse 
did develop but were broken off in sectioning. 

In all, 80 trees which contained one or both of these decays were 
dissected. The Trametes pini decay occurred alone in 61 of these, 
the dry-rot in small pockets in 11, and both forms in 8 trees. In 28 
of the 61 trees having the Trametes pini decay, this was either inter- 
mingled, graded into, or very close to pockets of typical decay without 
there being any line of demarcation between the two. In certain 
cases the two decays could be absolutely traced to the same source of 
infection. Tree No. 40 on the intermediate area forms an excellent 
example. This tree had two small open fire scars in the butt just at 
ground level. There was a light infection of typical pockets of dry-rot 
extending from ground level to a height of 7.3 feet. At this point 
Trametes pini decay appeared without any line of demarcation and 
182803°— 20— Bull. 871 3 



18 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 

extended to 29.4 feet, and then the typical pockets of dry-rot reap- 
peared, which ultimately ended at a height of 41.4 feet. The only 
possible means of entrance for the two forms of decay were the small 
open fire scars at the ground level. A similar condition is presented 
in tree No. 7 on the intermediate area. This tree had a large open 
fire scar extending from the ground level to a height of 8 feet. Typical 
dry-rot entering through this open wound began at 6 feet, extending 
to 9.7 feet, where it merged into Trametes pini decay, which then gave 
place to the typical dry-rot at 14.7 feet, and the latter finally ended 
at a height of 20.7 feet. No line of demarcation could be distinguished 
between the two decays, and the point of entrance of the infection was 
at the open fire scar. Other examples could be cited, but these seem 
sufficient. 

In the eleven trees in which the dry-rot in small pockets occurred 
it was either very close to or intermingled with typical dry-rot in six, 
and in four of these six trees both forms of decay could be exactly 
traced to a common point of entrance. There were no apparent lines 
of demarcation in any instance between the two forms of decay. In 
tree No. 392 in the intermediate range typical pockets of dry-rot 
extended from ground level to 28.7 feet. At this point the typical 
decay changed to the small pockets, and this form occupied the 
heartwood to 36.9 feet, where the decay stopped altogether. 

Finally let us consider the eight trees in which both the dry-rot in 
small pockets and the Trametes pini decay were found. In two of 
the trees the two decays occurred in different parts of the bole. In 
two trees the decays were very close together, while in four trees the 
two were accompanied by pockets of typical dry-rot. Tree No. 296 
on the intermediate area offers an excellent illustration of this last 
condition. In this tree the dry-rot in small pockets, the Trametes pini 
decay, and typical pockets of dry-rot were intermingled, and transi- 
tion stages between the three forms were apparent from ground level 
to a height of 30.3 feet. In four of the eight infected trees it was . 
possible to trace the entrance of both decays to the same point, 
healed fire scars. There were no lines of demarcation separating the 
various decays. 

The interesting point in connection with the two forms of dry-rot 
and the decay caused by Trametes pini is that they occurred in the 
same substrata, either merging into one another or actually inter- 
mingling without any well-defined lines between them. That such 
lines of demarcation between different decays are the general rule 
has long been accepted and has been most recently expressed again 
by Weir (31). Hence, it is particularly interesting to find two 
exactly opposite types of decay intermingling so freely. It is quite 
probable, however, that such occurrences in the future will come to 
be recognized as quite common. The writer has already found 



DRY-ROT OF INCENSE CEDAR. 19 

decays caused by Trametes pini and by Fomes laricis (the chalky 
quinine fungus) intermingled in the wood of living Douglas firs on 
several occasions, while down logs in the woods are often mycological 
gardens of wood-destroying fungi with the decays completely 
intermingled. 

Both the dry-rot in small pockets and the Trametes pini decay are 
nearly always fomid around decayed knots or following along healed 
wounds, mainly those caused by fire. Where the infections occur 
around knots the decay is almost invariably confined to the imme- 
diate neighborhood of the knot, resulting in little or no loss in the 
merchantable contents of the tree. Where any appreciable quantity 
of wood was rendered unmerchantable, the decays were almost 
invariably in intimate connection with healed-over wounds caused 
by fire, frost, or lightning, particularly the first, throughout their 
extent. Exceptions to this rule did occur. In one tree, for example, 
the Trametes pini decay extended for a distance of 23.5 feet in the 
center of the tree above an open fire scar without being in connection 
with any other wound. But the fire scar was very large, extending 
deeply into the tree and undoubtedly had a far-reaching influence 
on conditions in the heartwood. In another tree (tree No. 40 on the 
intermediate area; see p. 17) this same decay extended for 22.1 
feet in between two areas of typical dry-rot without following along 
any wound. The dry-rot in small pockets was found in one instance 
to extend for a distance of 8.2 feet, not in connection with a wound 
but merely as an extension of typical dry-rot. This case has already 
been cited (tree No. 302 on the intermediate area; see p. 18). 

The above fact suggests that the dry-rot in small pockets may be 
the result of the influence on the dry-rot fungus of changed condi- 
tions in the heartwood, either physical, chemical, or both, induced 
by the presence of wounds or knots. 

In further support of this hypothesis, it is almost invariably the 
rule wherever typical dry-rot is found along healed fire scars in the 
butt of a tree that instead of the pockets of normal size, one or more 
long continuous pockets of the dry-rot follow immediately along the 
scar throughout its length and invariably run out close to the end of 
the scar. A maximum length of 10 feet has been attained. Such 
pockets have never been found except in connection with wounds. 
This seems to prove that variations in the typical form of dry-rot 
may be induced by certain types of wounds in the tree. 

The fact that the Trametes pini decay is usually found in the 
immediate vicinity of knots or healed-over wounds may be taken to 
indicate that incense cedar is an unsuitable host for Trametes pini 
and that the organism can rarely progress much beyond the point of 
infection. This would also explain the rare production of sporo- 
phores and the fact that in the only known collection, to cite Weir's 



20 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 

words in a letter to the writer, "The sporophores are of the small 
depauperate type which I find occasionally on trees at high eleva- 
tions or on old punk knots from which the original sporophores have 
fallen and are reviving." 

However, for the purposes of this paper these decays may all be 
treated as one and the same, since the dry-rot in small pockets and 
the Trametes pini decay are of negligible importance both in the 
number of infections and amount of cull resulting. Hence, except 
in the data on the rate of spread of the dry-rot, they are included in 
all subsequent pages with the typical decay of Polyporus amarus. 

No relation was found between the width of the sapwood and the 
extent of decay: trees with wide and narrow sapwood seem to be 
equally affected with the dry-rot. 

RAPIDITY OF SPREAD OF THE DRY-ROT. 

Although the rapidity of the spread of decay caused by heartwood- 
inhabiting fungi in standing trees has always been of interest, very 
little work has been done on this line. Hartig (9, p. 115-116), 
mentions this briefly in relation to the rot caused by Polyporus 
(Fomes) igniarius in oak. More recently Munch (23) has published 
some interesting results from studies of the same fungus and host, 
showing a wide variation of 3.8 to 37.5 cm. (0.12 to 1.23 feet) in 
the yearly vertical progress of the decay, with an average of 5 to 9 cm. 
(0.16 to 0.30 of a foot). No tangible difference was found between 
the upward and downward rate of spread from the point of infection. 
Munch's results are based on an analysis of only 15 cases, and 
their value is further reduced by the fact that in determining the 
age of the infection which entered a tree through an open wound, he 
assumed that infection must have occurred the year the wound was 
made, or at least a very few years subsequently, even though the 
wound was still open at the time of analysis. True enough, as 
shown by Munch (23), Fomes igniarius attacks not only the heart- 
wood but the sapwood of many trees and kills the cambium, causing 
cankers with subsequent callusing, and by counting the number of 
annual rings in the callus at the point of infection the age of the 
decay can be determined, provided a canker was formed the year of 
infection; but this is not uniformly the case, to judge from Munch's 
(23, p. 519) own statement that " Fomes igniarius produces exceed- 
ingly variable cankers. Sometimes small points of infection which 
are scarcely noticeable and are soon healed perfectly ..." 

In securing the figures on the yearly rate of spread of the dry-rot, 
only those infections were considered the entrance of which could 
be absolutely traced, without any other possibilities, to a healed 
scar for which it was possible to determine the exact dates of 
occurrence and closure. For example, an infection is found in a 



DRY-ROT OF INCENSE CEDAR. 21 

tree which was cut in 1915. The fungus entered through a healed 
fire scar which occurred in 1781 and was completely closed by callus- 
ing in 1816. B} r subtracting 1781 and then 1816 from 1915 it is 
seen that the fungus has been in the heartwood a minimum of 99 
and a maximum of 134 years. During this period resulting decay 
has progressed a vertical distance of 34.2 feet in the bole, or a yearly 
average of 0.25 to 0.34 of a foot. The radial extent of the decay is 
disregarded, since this is of little importance from a practical view- 
point. Any serious infection usually extends more or less through- 
out the heartwood in a radial direction. Of course, the above 
method does not give a single figure for the yearly average progress 
of the dry-rot, but it does give the exact minimum and maximum 
limits between which the true figure lies. 

In all 99 infections were possible of analysis by this method. 
The great majority of these commenced at ground level, entering 
through fire scars and extending up the bole. Ten of the infections 
were traced to wounds high enough up on the trunk, however, to 
make possible a comparison of the upward and downward progress 
of the diy-rot. This meager basis indicated that the dry-rot, in the 
main, progresses more rapidly downward than upward, although 
in individual cases this relation may be reversed. 

The yearly progress of the decay is exceedingly variable. At one 
extreme there is a tree in which the fungus had been vegetating be- 
tween 124 and 135 years, but the resulting dry-rot had only attained 
a length of 0.4 of a foot, or a minimum average yearly progress of 
0.002 and a maximum of 0.003 of a foot. The tree was 147 years 
old. At the other extreme, the fungus in from 10 to 58 years caused 
decay extending over 30.9 feet of the bole of another tree, that is, a 
minimum average progress of 0.53 of a foot a year and a maximum 
of 3.09 feet. This tree was 240 years old. Again, in a 107-year-old 
tree the fungus caused a decay with a minimum average progress 
of 0.87 of a foot and a maximum of 1.90 feet a year, extending a 
total of 40 feet vertically. In the main, however, the minimum prog- 
ress of the dry-rot varied from 0.01 to 0.20 of a foot a year, while the 
maximum ranged from 0.01 to 0.35 of a foot. Higher yearly rates 
than the upper limits stated were not uncommon, but lower rates 
than 0.01 of a foot were rare. 

These figures clearly demonstrate the slow progress of the dry-rot 
fungus in causing decay. Generally it required from 50 to 300 years 
to bring about any far-reaching dry-rot. In the heartwood of cer- 
tain individuals the fungus had vegetated for decades, the resulting 
decay only extending 1 or 2 feet from the point of infection. A 
similar condition was found by Munch (loc. cit.) for Polyporus (Forties) 
igniarius attacking oak. As to why the development of the dry-rot 
fungus in certain cases is so inhibited the writer is unable to present 



22 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 

any definite information, but certainly the chemical and physical 
condition of the substratum must have a strong bearing on this 
phenomenon. Hartig (9, pp. 115-116) believes in the case of Poly- 
porus (Fomes) igniarius that the width of the annual rings of the 
wood is not without influence on the rapidity of decay. Munch (20, 
p. 156) states that the more rapidly grown coniferous wood, conse- 
quently that with the broader annual rings, is more speedily decayed 
by Fomes annosus than slower grown wood with narrower rings, even 
extending this to broad and narrow rings in the same individual. 
Later (22, p. 403-406), he shows that suppressed individuals of beech 
artificially infected with Stereum purpureum. S. rugosum, Polyporus 
(Fomes) igniarius, and P. (F.) fomentarius were more seriously de- 
cayed than dominant thrifty trees, yet it is just such suppressed trees 
which must have the narrowest annual rings. Finally (23, p. 521), 
the same investigator finds no relation whatsoever between the 
breadth of the annual rings and the rapidity of decay in the wood of 
oak attacked by Polyporus ( Fomes) igniarius. 

PURPLE COLORATION. 

Accompanying the dry-rot is a purplish coloration of the heartwood 
which is very characteristic. The writer does not find this mentioned 
in any description of the dry-rot so far available, but it is well known 
to the lumberman. This color varies from a light salmon-red or pink 
to a pronounced purplish red in trees with heavy decay, where it may 
stand out strongly in cross section as a ring surrounding the decayed 
area or present a mottled appearance over the entire heartwood. 
Where the coloration is faint it is sometimes impossible to detect it 
in cross section, but if the tree is split longitudinally the color is 
readily apparent, although it often fades out entirely after several 
days' exposure to light and air. It usually commences at ground 
level and extends upward, but may start at varying heights. 

Microscopical studies of this colored wood did not show any devia- 
tion from sound wood. No hyphse were found except at points im- 
mediately adjacent to pockets of dry-rot. No chemical or physical 
examination was possible. 

In all, 634 trees were dissected in which the purple coloration was 
present. The notes from Cow Creek did not include data on this 
coloration. The youngest tree in which the coloration was present 
had an age of 72 years, while the youngest tree cut was 52 years old. 
No attempt can be made to set a minimum age limit for trees with 
purple coloration, since not many trees were cut below the age of 
70 years. 

Of the 634 trees under consideration, the purple was present in 84 
in which no dry-rot was found. In these the coloration, varying 
through all shades from a very faint salmon pink to pronounced red- 



DRY-ROT OF INCENSE CEDAR. 23 

dish purple, usually began at the ground level, extending up the heart- 
wood to a minimum height of 2.6 feet and a maximum height of 31.4 
feet. Of these trees 39 had open or healed-over wounds, mainly- 
caused by fire, offering or having offered a means of access for the 
dry-rot, but the remaining 45 were without indications of wounds, 
the only possible mode of entrance for the decay being through 
branch stubs. It would be highly improbable that all of these trees 
could be infected by the dry-rot fungus without showing any indica- 
tions of decay, so the conclusion is obvious that purple coloration 
may exist unaccompanied by Polyporus amarus. 

In all, 510 trees with typical dry-rot alone or in conjunction with 
secondary decay were worked up at Sloat, Strawberry, and Crockers 
Station. Notes on 25 of these were incomplete so far as purple 
coloration is concerned, so they drop out of consideration. All but 
17 of the remaining 485 had purple coloration accompanying the 
decay. In certain cases the coloration did not extend over the entire 
decayed area, running out before the decay ended, or else isolated 
pockets of dry-rot were found outside the area of coloration. In the 
17 cases of dry-rot unaccompanied by any coloration, the decay as a 
rule was negligible. In four of these trees, however, there was a loss 
in volume caused by the dry-rot of 7.1, 21.3, 39, and 67 per cent, 
respectively, without any coloration being visible, indicating that 
serious decay can exist apart from the purple coloration. 

Of the 59 infections of the Trametes pini decay, 4 became impos- 
sible of consideration because of incomplete notes. Of the remaining 
55, 12 were unaccompanied by purple coloration, but all of these 
except two were very superficial infections. Even in these two the 
amount of cull was very small. This decay had already been shown 
almost invariably to follow wounds in the trees; hence, it becomes 
quite reasonable to presume that the absence of purple coloration 
was brought about in most instances by the change in the physical or 
chemical condition of the heartwood induced by the influence of the 
woimds. 

Where the typical decay and the Trametes pini decay were inter- 
mingled the coloration was almost invariably present, although not 
always throughout the entire infected wood. This was also the case 
with the brown dotlike pockets. However, these data should not be 
judged as more valuable than indications, since the number of cases 
available was relatively few. 

Secondary rots comprised 43 infections; only 12 of these were in 
conjunction with purple coloration. The 31 without coloration only 
yielded one cull case;, the an\ount of unmerchantable volume was 
very small, and furthermore these secondary rots were almost invari- 
ably in connection with healed or open wounds. 



24 BULLETIN 811, U. S. DEPARTMENT OF AGRICULTURE. 

Hence, on account of the failure to find any microscopical evidence 
of fungous action in purple wood, the presence of dry-rot outside the 
area of purple coloration in certain trees, the frequent occurrence of 
extensive coloration in trees free from dry-rot, combined with the 
usual presence of the purple coloration in wood badly enough decayed 
by Polyporus amarus to cause a noticeable reduction in the merchant- 
able contents of the individual tree, while it may be more often absent 
in light infections, the conclusion appears obvious that purple colora- 
tion is not a result of the action of the fungus, but, on the contrary, 
if it bears any relation whatever to the dry-rot, is merely a condition 
of the heartwood inducing favorable development of the vegetating 
hyphse. The fact that the Trametes pini decay is more often unac- 
companied by the coloration is offset by such infections usually being 
superficial and following wounds which probably exert a profound 
influence on the heartwood. No relation was found between the 
purple coloration and the width of the sapwood. Trees with sap- 
wood varying from very narrow to very broad alike had the colora- 
tion in the heartwood. 

RELATION OF DRY-ROT TO AGE AND CONDITION OF THE TREE. 

From previous hints in the literature (22, p. 403-406; 23, p. 520; 
16, p. 18-19, footnotes), Meinecke's preliminary study on incense 
cedar and his later work on white fir (16), it was reasonable to assume 
that some relation should exist between dry-rot and the age and 
condition of the tree; i. e., the degree of dominance and suppression. 

Munch (22, p. 405), working with artificially infected red beech, 
found suppressed trees more susceptible to decay by Polyporus 
(Fomes) igniarius, P. (F.) fomentarius, Stereum rugosum, and S. pur- 
pureum than thrifty, dominant ones and explains this by the theory 
that the wood of suppressed trees contains a greater amount of air, 
consequently more oxygen, than thrifty dominants. In previous 
experiments the same investigator (19, 20, 21) had brought out the 
strongly favorable influence of oxygen in the host tissues on the 
development of wood-inhabiting fungi. Meinecke (16, p. 48) recog- 
nizes three periods in the life of white fir in its relation to the stringy 
brown-rot caused by the Indian-paint fmigus (Echinodontium tinc- 
torium): (1) The age of infection, at which "the infection rarely leads 
to more than negligible decay unless the tree is handicapped by quite 
unusually severe conditions, such as very large old wounds;" (2) the 
critical age, which "marks the point after which a combination of 
pronounced suppression and heavy wounding generally results in 
distinct decay;" and (3) the age of.decline, "when even dominant 
(that is, thrifty) trees become subject to extensive and intensive 
decay." The relation between decay and suppression is brought out. 



DRY-KOT OF INCENSE CEDAR. 25 

The crown class, as determined by observation of the standing 
tree, expresses the past history, more or less strongly modified by 
conditions prevailing through a varying number of years previous to 
the time of observation; it may not give the real past history of the 
tree. "Dominance" and "suppression" are really incorrect terms, 
used for lack of better ones. They are based on the relation of the 
height of one tree species to others in the same stand. In this case 
height alone would be misleading. For example, consider a more or 
less second-story species in a mixed stand, in which category incense 
cedar falls. Practically all the trees would be included in the inter- 
mediate or suppressed classes when related to other species in the 
stand, thus entirely obscuring the true relation of the individuals 
within the second-story species. On the other hand, it is an exceed- 
ingly difficult undertaking, often leading to grave error, to attempt 
classification by the observation of individuals in a mixed stand 
with relation to other individuals of the same species. 

For our purposes we can not consider other tree species, but must 
compare individual trees with others of the same species. But here, 
also, height alone is not the deciding factor. Instead of giving 
dominance and suppression in the current meaning, these terms are 
expressed by the relation of the actual volume of the tree to the 
average volume of trees of the same age. Therefore, it was necessary 
to "curve" data collected on a number of trees to secure average 
volumes by age. Only trees of normal form with exact ages and free 
from severe wounds, malformations, and other seriously injurious 
factors which would interfere with the correct computation of the 
volume were used. Curves were constructed for the intermediate 
area and for the optimum area, since it was apparent that the 
volumes by ages would be much higher for the last-named areas 
than for the first, which fact was strongly brought out by the result- 
ing curves. These curves are presented in figure 1, the higher curve 
based on 461 trees representing the optimum area and the lower 
based on 340 trees, the intermediate area. The National Forests on 
which these areas were located are also indicated. Thence, the trees 
for the intermediate area and for the optimum area were rated in 
regard to their respective curves, those with a volume higher than the 
average given by the curve for the same age being classed as dominant 
and those with a lower volume as suppressed. At first, an inter- 
mediate group was selected by designating an arbitrary volume above 
and below the average volume, trees between these limits being 
classed as intermediate. However, it was found that such trees 
inclined either toward the dominant or the suppressed hi their charac- 
teristics, depending on whether they were above or below the average 
in volume for the same age. Furthermore, it was exceedingly difficult 
182803°— 20— Bull. 871 1 



26 



BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 



to determine just what the limits of the intermediate class should he, 
so in order to preclude any error in judgment the procedure as first 
stated of establishing just two classes, dominant and suppressed, to 
include all the trees, is followed throughout. 

The method of obtaining the volume of the tree in cubic feet 
requires a little explanation. Each tree was considered as a perfect 
cone over the stump, at which the age count had been taken, in 
order to obtain directly comparable figures for the different ages. 
Figures from normal trees showing the relation of the diameter 
breast high to diameter of butt at stump height (1.5 feet) were plotted 
and curved, the strongest portion of this curve lying between 10 and 
50 inches diameter breast high. From this curve a table expressing 



tea 






































iAO 
































J& 


rmislaus. 


























ft.O 
























1 
















p 






































i 


















um c 


*) m 




1 

V 60 
A) 

a 


































JPi. 


























eJjS- 


<*£ 


rjt* 
































V 


£C2 




















I 


























































































































«o 










































































*\ 




c 















































40 SO 12.0 160 ZOO Z40 £60 3SO 360 4OO 

Age -years 
Fig. 1.— Comparison of average volumes of incense cedar on the optimum and intermediate areas. 

the relation of the diameter breast high to diameter of butt at stump 
height for each inch class was read. It was then a simple matter to 
secure the diameter outside the bark at stump height for any tree, no 
matter how irregular the stump might be, due to wounds or other 
factors, and combining this with the height to work out the total cubic 
contents. Loss of volume caused by wounds or other factors was dis- 
regarded. In other words, each tree was treated as if it was absolutely 
normal. Let it be emphasized again that the volumes obtained were 
not meant to be an exact expression of the actual volume of each 
tree to the last cubic foot but merely had to be directly comparable 
to each other for the various ages. 

In considering the trees with decay, each separate focus of dry-rot 
is termed an infection, and there may be two or more infections in 



DRY-ROT OF INCENSE CEDAR. 27 

the same tree, each one, however, the result of a separate and distinct 
inoculation. As soon as an infection causes a measurable amount of 
cull it becomes a cull case and is so termed. Hence, every infection 
is not a cull case, but every cull case is an infection. Only loss of 
merchantable timber through dry-rot is considered; cull from 
wounds, knots, limbs, insect borings, or crook is disregarded, since 
these have no bearing on the loss from dry-rot except when the 
decay is directly traceable to a wound. In such cases loss from the 
wound is included with the volume of rot. 

For figuring from the field notes and measurements the cull caused 
by dry-rot, the amount and degree of damage with relation to the 
resulting loss in merchantable lumber was carefully taken into 
account, just as it is in scaling. For example, a cull case might 
have considerable linear extent but consist only of a few scattered 
pockets in a straight line, resulting in little or no loss in merchantable 
volume. The same number of dry-rot pockets, shorter in linear 
extent but radially scattered throughout the heartwood, probably 
would cause considerable cull. Again, a number of pockets close to 
the sapwood, mostly slabbing out when the log is sawed, would have 
far less weight than the same pockets in the center heartwood. 
Meinecke's method (16, p. 37) of considering the entire bole of the 
tree over the linear extent of decay as cull, while justifiable with the 
commercially inferior white fir, could not be applied to the distinctly 
more valuable incense cedar. Here the lateral extent of the decay 
also had to be taken into account. This could be readily determined 
from the field notes and diagrams. For example, if the decay occu- 
pied one-fourth of the area as seen on cross sections and had a linear 
extent of 10 feet, the volume outside the bark of this 10-foot frustum 
(the tree being considered as a cone, see p. 26) was first secured 
and then one-fourth of it was considered as the volume of the decayed 
portion of the tree. Below one-fourth the decay was usually treated 
as negligible except when it had a linear extent of several feet. The 
volume was then computed as before. 

Separate tables containing the above figures were worked up for 
the four areas, the trees being arranged progressively by ages, begin- 
ning with the youngest. It does not seem necessary to present these 
tables, since they were merely preliminary. 

In considering the trees on the intermediate area it was found that 
the first infection which resulted in cull occurred in a tree 98 years 
old. However, infection can take place at a much earlier age than 
this. For example, in a tree 104 years old there was a light cull case 
traced to a healed lightning wound. The tree was injured at the 
age of 50 years and the wound completely healed when the tree was 
63 years old; hence, the tree could not have been older than 63 years 
at the time of infection. Again, in a tree 146 years old there was a 



28 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 

serious cull case traced to a healed fire scar. This wound healed 
when the tree was 38 years old; hence infection could not have 
occurred subsequent to that age, since the field notes seem to exclude 
any possibility of an entrance of the dry-rot through a knot. Numer- 
ous other examples might be cited, but none of them reduces the 
mini mum age of possible infection below 38 years. 

An analysis of infections definitel} 7 " traced to healed wounds in 
trees on the optimum area places the earliest age at which trees may 
be infected at 34 years, and this may be accepted as the age of infec- 
tion for all the areas, since there is no apparent reason other than 
chance as to why the various areas should differ in this respect. 
Infections were very common between the ages of 45 and 80 years. 
No tendency was apparent toward an earlier age of infection in 
suppressed than in dominant trees, or vice versa. The foregoing 
figures are based on an analysis of 99 infections. Of course, this age 
may be even lower than here indicated, but it is evident that the 
earliest age of infection can not be lower than the age at which heart- 
wood formation takes place in incense cedar. Just when this occurs 
is not definitely established, but observation seems to place it some- 
where around 20 to 30 years. To be sure, there is a possibility of 
infection taking place in pathological heartwood resulting from an 
injury before the true heartwood is formed, the fungus mycelium 
vegetating in this type of heartwood until such time as true heart- 
wood develops and then attacking it. While absolute proof of this 
course of procedure is lacking, observations have all tended toward 
substantiating the theory. 

Furthermore, this age agrees approximately with that found by 
other workers with different species. Meinecke (16, p. 47) finds 
that for white fir (Abies concolor) decay caused by the Indian-paint 
fungus (Echinodontium tinctorium) "may show in trees 60 years old 
or perhaps younger," while Weir and Hubert (32, pp. 17-18), working 
with the same fungus in western hemlock (Tsuga TieteropJiylla) , set 
the average infection age for one type at 44.5 years and for another 
at 57.3 years. The figures are obtained by the use of a formula 
applied to the younger age classes. These same workers (33, pp. 
11-12) place the "age of earliest infection" at about 50 years for 
western white pine (Pinus monticola) attacked by several common 
wood-destroying fungi. 

Interesting as the determination of the age of infection or the age 
of earliest infection may be from an academic viewpoint, it is of little 
practical importance in this region. The questions of real import 
in this as in other species are the age at which decay begins to result 
in cull of economic importance and whether there is any relation 
between this and dominant and suppressed trees. The trees on the 
intermediate area and on the optimum area were first arranged 



DRY-ROT OF INCENSE CEDAR. 29 

by 40-year age classes, grouping dominant and suppressed trees 
separately, and the percentage of dry-rot was determined for each 
age class. This was done by relating the total volume of dry-rot 
in each age class to the total volume in cubic feet of the trees in that 
age class. From these fclbles it was apparent that while there was 
no tangible difference between the amount of decay in the dominant 
and suppressed trees on the intermediate area, on the optimum area 
there was a decided difference, most strongly shown in the younger 
age classes, the dominant group having a lower percentage of decay 
than the suppressed trees. 

That the trees in the intermediate area fail to bear out the relation- 
ship between suppression and decay indicated by the results of other 
workers on different species is after all logical. The reason for this 
is not hard to find. These trees are in the intermediate range for 
incense cedar, where the growth on the whole is relatively slow, and 
while they may be placed in dominant and suppressed groups within 
themselves, yet in relation to the trees in the optimum range they 
are slow growing, practically all being included under suppressed, 
with a few dominants. In other words, most of these trees are under 
the influence of regional suppression. Another glance at figure 1, 
which shows the great disparity between the volume-age curves for 
the two regions, brings this out more clearly. The term "regional 
suppression" is a new one. However, the concept which it embraces 
has long been advanced in ecology and silviculture. That there is 
a marked decrease in vigor and a decline in the rate of growth for 
each tree species outside its optimum, becoming greater as the dis- 
tance from the region of best development increases, until finally 
the species becomes completely suppressed by other species either 
in or closer to their own optimum, has been pointed out by Mayr 
(13, pp. 73-79). This is exactly what has happened to incense cedar 
in the intermediate range. At best a second-story tree, in this 
region, away from its optimum, it has become, except for a few 
scattered individuals, badly suppressed by Douglas fir, Jeffrey pine, 
and yellow pine, which, while not in their own optimum, are yet 
closer to such a condition than the incense cedar. Mitchell (17, p. 33) 
recognizes how far this may go in suggesting that it may be advisable 
to eliminate the species entirely on the sites less adapted to it. 

An analysis of the field notes reveals that this regional suppression 
is not due to a pathological condition, which might be suspected from 
the presence of the mistletoe (PJioradendron junijyerinum libocedri) or 
of the needle and twig parasite (Gymnosporangium blasdaleanum) . 

A comparison of the trees on the intermediate area with the volume- 
growth curve for the optimum area resulted in the classification of 
only 38 out of the total of 495 trees as dominant. In other words, 
457 of the trees on the intermediate area are actually suppressed 
when compared to the average for the optimum area. 



30 



BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 



It is not to be expected that the growth habits of the dry-rot 
fungus would vary to any extent in regions so closely related 
climatically as the intermediate and optimum ranges of incense cedar; 
therefore, it is reasonable to believe that no matter what the classifi- 
cation of the trees on the intermediate area may be in respect to 
dominance and suppression when compared with the volume-growth 
curve for that area, to find the true relation of the dry-rot fungus to 
dominant and suppressed trees it will be necessary to determine the 
classification of each tree by comparison with the volume-growth curve 
for the optimum area. 

This is brought out in Table II, in which the trees from all the areas 
are combined, the dominance or suppression of all the trees being 
determined by comparison with the volume-growth curve for the 
optimum area. Only trees in which the progress of the decay or a 
fire scar did not make it impossible to determine the age at stump 
height are included in this table. This explains the slight dis- 
crepancy between the total number of trees dissected and the total 
number included in this and subsequent tables. 

Table II. — Cull caused by dry-rot found in incense cedars of the combined areas. 



Age class. 



Number of trees 
(basis). 



Average age. 



Dominant. 



Suppressed. 



Dominant. 



Cull caused by dry-rot 
(percentage of the 
total volume). 



Suppressed. Dominant 



Suppressed. 



to 40 years. . . . 
41 to 80 years... 
81 to 120' years.. 
121 to 160 years. 
161 to 200 years. 
201 to 240 years. 
241 to 280 years. 
281 to 320 years. 
321 to 360 voars. 
361 to400vears. 
401 to 440 year's. 

Combined 



1 
43 

125 

218 

191 

84 

79 

42 

16 

2 

2 






74 
105 
142 
180 
223 
26S 
301 
:m 

372 



803 



40 
57 
105 
140 
179 
222 
258 
294 
332 
368 
436 



In Table II the dry-rot percentage in the age class 161 to 200 
years, for example, is figured on the total volume of all the dominant 
trees both sound and decayed in that age class and not on the total 
volume of both dominant and suppressed trees. This is the method 
used throughout the table. 

It will be noticed that the number of trees (basis) in the suppressed 
class far exceeds the dominant, this being a direct result of the 
influence of regional suppression on the trees of the intermediate area. 

The columns of greatest interest are the last two, in which the 
dry-rot percentages of the dominant and suppressed trees in the 
different age classes are directly comparable. By dry-rot percentage 
is meant the percentage of cull caused by the decay resulting from 



DRY-ROT OF INCENSE CEDAR. 



31 



the work of the dry-rot fungus. The reader should remember that 
the percentage of cull based on the merchantable volume of the trees 
would be higher than the percentages here given, since these are based 
on the total volume of the trees outside bark and including the entire 
top. In the younger age classes up to 160 years the percentage of cull 
is small and variable, in one class higher in the suppressed, in another 
higher in the dominant, and in a third equal. But in the age class of 
161 to 200 years a decided jump in the percentage of cull occurs, 
particularly in the suppressed trees. While the increase in the case of 
the dominants is only 3 per cent, in the suppressed trees it amounts to 
8 per cent, bringing the cull percentage to 12. In the next age class 
a still further change is apparent. Here the cull percentage in the 
dominant trees increases strongly, as does also the percentage in the 
suppressed trees, the latter still remaining considerably higher than 
the former. But in those subsequent classes which have a sufficient 
numbers of trees to make the data of value, the cull is higher in the 
dominant than in the suppressed trees. When the age classes are 
combined, the total cull is 4 per cent more in the suppressed than in 
the dominant trees. 

The salient features shown by Table II are the low percentage of 
cull in the younger age classes, the sudden increase earlier in the 
suppressed than in the dominant trees, which after it once begins goes 
steadily on with advancing age, and the higher percentage of cull in 
the suppressed trees as compared with the dominant trees in the two 
age classes which show the first sudden increase in this percentage. 

However, the percentage of cull caused by dry-rot is not the only 
figure of interest, since it is prerequisite that the trees first be infected 
and that these infections develop sufficiently to cause measurable 
cull. Table III gives the figures on percentage of infection and cull 
cases. The number of trees used as the basis and the average age 
are the same as in Table II. 

Table III. — Infections and cull cases found in incense cedars of the combined areas. 



to 40 years .... 

41 to 80 years 

81 to 120 years... 
121 to 160 years.. 
161 to 200 years.. 
201 to 240 years.. 
241 to 280 years. 
281 to 320 years.. 
321to360vears. 
361 to 400 years.. 
401 to 440 years.. 

Combined. 



Ace class. 



Infections (percentage 
of total number of 
trees). 



Dominant. Suppressed 



12 

50 

62 

57 

71 

87 

100 

100 

100 




5 
33 
42 
62 
74 
82 
90 
87 
100 
100 



Infections causing meas- 
urable decay (percent- 
age of t otal cull cases ) . 



Dominant. Suppressed. 




28 
35 
36 
56 
80 
86 
100 
100 





5 

15 

28 

44 

63 

78 

88 

87 

100 

100 



32 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 

Table III shows that the percentage of infections is not in exact 
relation to the percentage of cull caused by dry-rot as given in Table 
II. In the age class of 41 to 80 years, while the percentage of 
infections is higher in the dominant trees the percentage of cull is 
slightly lower. In the age class of 81 to 120 years these percentages 
bear the same relation to each other as they do in all other classes 
except the classes of 121 to 160 years and 361 to 400 years. In the 
former there is a much higher percentage of infections in the dominant 
trees, while the percentage of cull is equal, and in the latter the per- 
centage of infections is the same in both dominant and suppressed 
trees, while the percentage of cull is higher in the former. For all the 
age classes combined the percentage of infections is markedly higher 
in the dominant than in the suppressed trees. 

Now, considering the columns relating to the total trees with cull 
cases, that is, where infections cause a measurable amount of decay, 
it is found that in the age class of 41 to 80 years none of the infections 
in the dominant trees result in cull cases, while all of the infections in 
the suppressed trees do, thus accounting for the higher percentage of 
cull in the suppressed trees in that class. In the next age class (81 
to 120 years) the dominant trees have almost twice as many cull cases 
as the suppressed, and the percentage of cull is just twice as great in 
the former. But in the age class of 121 to 160 years, while the cull 
cases are in a higher percentage in the dominant trees the percentage 
of cull is equal in the two classes, showing that there is more loss per 
cull case in the suppressed than in the dominant trees. In the subse- 
quent age classes the cull cases and the percentage of cull are in the 
same general relation except in the age class of 361 to 400 years, 
where the difference is the same as explained for the infections. The 
total cull cases for the suppressed trees is only 1 per cent higher than 
for the dominant trees. 

The idea might have been advanced that since inoculation by 
spores of any wood-destroying fungus is to a certain extent a matter 
of chance, the greater percentage of cull in the suppressed trees might 
have been due to a greater number of infections in these trees. But 
Table III shows more infections in the dominant trees, while the cull 
cases are about equal in both. Therefore the cull cases must be 
more severe in the suj)pressed trees. 

The infections, or even the cull cases, do not show the same pro- 
gression through the age classes from the youngest to the oldest as is 
shown by the cull percentage. In the former the sudden, sharp 
increase in the age class of 161 to 200 years for the suppressed and in 
the class of 201 to 240 years for the dominant trees is not apparent. 
The increase is more regular throughout, thus indicating that there 
is an influence other than merely the number of infections which has 



DRY-ROT OF INCENSE CEDAR. 



33 



a strong bearing on the development of cull cases and the percentage 
of cull. 

Since neither the total number of infections nor cull cases follows 
the same law as the percentage of cull, it is self-evident that there 
must be an exact relation between this last and the more extensive 
or severe cull cases. Accordingly, in Table IV the severe cull cases, 
that is, those cases in which one- third or more of the total volume of 
the tree is a loss through dry-rot, are considered separately. The 
same basis is used as in Tables II and III and the percentages are 
based on the number of trees in the dominant and suppressed groups 
considered separately in each age class. 

Table IV. — Relation between dominant and suppressed trees in severe cull cases found in 
incense cedars of the combined areas. 



Age class. 


Severe cull cases (per 
cent). 


Age class. 


Severe cull cases (per 
cent). 




Dominant. 


Suppressed. 


Dominant. 


Suppressed. 








2 
2 
14 
31 
48 


281 to 320 years. . . 


71 
67 
100 


66 


41 to 80 years 



3 
2 

5 
26 
73 


321 to 360ryears 


81 


81 to 120 years 


361 to 400 years... 


50 


121 to 160 years 




100 


161 to 200 years 








201 to 240 years 


14 


17 


241 to 280 years 













In Table IV is seen the same form of progression for the severe cull 
cases as was shown for the amount of cull in Table II. Low per- 
centages in both groups up to an age of 160 years, with a sudden 
increase in the percentage of severe cull cases in the age class of 161 to 
200 years for the suppressed group are followed by a like increase in 
the class of 201 to 240 years for the dominant trees. After 240 years 
is passed there is a higher percentage of severe cull cases for the sub- 
sequent age classes in the dominant group, just as is the case for the 
percentage of cull. The only exception to this is found in the class of 
321 to 360 years, where the relation is reversed. 

The outstanding fact shown by Tables II, III, and IV is that incense 
cedar during the earlier stages of its life, even though heavily infected, 
is able to retard the progress of the dry-rot fungus in causing decay. 
Then comes a period, earlier in the case of suppressed than of domi- 
nant trees, at which the progress of the fungus can no longer be held 
in check and the trees become subject to severe decay, with the accom- 
panying high percentage of cull. In other words, the decay becomes 
extensive. This period occurs in the age class of 161 to 200 years in 
the suppressed group and in the age class of 201 to 240 years in the 
dominant group. An analysis of the individual trees, in a table which 
is too long to present here, reveals the fact that this change begins at 
167 years in the suppressed and at 214 years in the dominant trees, 



34 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 

At these ages extensive decay, as represented by severe cull cases, 
becomes common in the individuals of the respective groups. These 
ages, using Meinecke's nomenclature, may be termed the "critical 
age" and "age of decline" for incense cedar — that is, the ages at 
which suppressed trees and dominant trees, respectively, become 
subject to extensive decay. Meinecke found a combination of severe 
wounding and pronounced suppression both contributing to the criti- 
cal age in white fir, but in incense cedar wounding is not necessarily 
a factor. This will be brought out later when mechanical injuries are 
considered. 

After the age of decline is passed, as shown by the percentage of 
cull in the classes older than 240 years, the dry-rot is more extensive 
in the dominant than in the suppressed trees. This means that 
while the dominant trees are able to ward off the extensive develop- 
ment of the dry-rot fungus for a longer period than the suppressed 
trees, after the age of decline is once passed dominance ceases to be 
a factor in resisting decay and, in reality, seems to favor it. This 
may be due to the fact that in the old, overmature dominant trees 
there is a higher percentage of food material (i. e., heartwood) for 
the fungus to work on in relation to the total volume than in the 
case of the suppressed trees. The fungus does not attack sapwood. 

Let us consider what the foregoing paragraphs mean from a prac- 
tical standpoint. Roughly, we may place the critical age at 165 
years and the age of decline at 210 years. This does not mean that 
there is no loss from decay previous to these ages, or even that 
there are no severe cull cases; but the latter are so rare, as shown by 
Table IV, that they may well be regarded as exceptions. Since all 
but a very few of the trees on the intermediate area are suppressed, 
taking this area as representative for the intermediate range we 
can not expect trees within this range to remain free from extensive 
dry-rot after they have attained the age of 165 years. In the opti- 
mum range this same age may be set for suppressed trees, while 
dominants will remain relatively sound until the age of 210 years is 
reached. On the optimum areas dominant individuals comprised 
36.5 per cent of the total, but on the intermediate area only 7.6 per 
cent. 

No relation was found between diameter breast high and dry-rot. 
This could hardly be expected, considering that incense cedar is a 
tolerant species in an uneven-aged mixed stand. 

In Tables II, III, and IV the comparison of the dominant and sup- 
pressed trees in their relation to the percentage of cull due to dry-rot 
has been emphasized to the neglect of other considerations in which 
the same relation might be found in both groups. In Table V many 
of the data given previously but separately for the dominant and 
suppressed groups are combined. 



DRY-ROT OF INCENSE CEDAR. 35 

Table V. — Combined data relating to dry-rot found in incense cedars of the combined areas. 



Age class. 



Average 

age 
(years). 



Number 
of trees 
(basis). 



Percentage of— 



Dry-rot 
volume. 



Severe 
cull 

cases. 



Cull 
cases. 



Infec- 
tions. 



to 40 years — 
41 to 80 years... 
81 to 120 years. . 
121 to 160 years. 
161 to 200 years. 
201 to 240 vears. 
241 to 280 years. 
281 to 320 years. 
321 to 360 years. 
361 to 400 years. 
401 to 440 years. 

Combined 



40 
60 
105 
141 
ISO 
223 
259 
296 
334 
370 
436 



1 

51 

185 

284 

233 

118 

94 

49 

19 

4 

2 




4 
20 

29 

42 
61 
79 
88 
90 

too 

100 




6 

38 
46 
61 
73 
83 
92 
90 
100 
100 



1,040 



Table V strikingly demonstrates the cumulative risk to incense 
cedar from dry-rot with advancing age. Starting at 1 per cent of 
cull in the age class of 41 to 80 years it mounts to 67 per cent in 
the class of 321 to 360 years. With a very gradual increase up to 
160 years it then becomes rapid. The figure of 82 per cent in the 
class of 361 to 400 years, even though on an insignificant basis, is 
not without significance when considered in relation to the general 
previous progression. That this figure should drop to 5 per cent in 
the last age class need not cause concern, since the basis is only two 
trees. Even though infected, a tree may escape extensive decay 
throughout its life. This is a rare occurrence, however. The percent- 
age of severe cull cases closely follows the percentage of cull throughout 
until the last two age classes with their small bases are reached. 
These two sets of figures show beyond doubt the high percentage of 
loss through dry-rot that may be expected in overmature cedars and 
clearly prove that the presence of such trees in our stands of the pres- 
ent and the future can be nothing but an economic loss. 

That the percentages of cull cases and of infections do not follow 
the same form as the two others just discussed was shown in previous 
tables, but is more clearly brought out here. The reasons for this 
have been touched upon. However, these two figures are of interest 
when compared. It is seen that with advancing age the percentage 
of cull cases becomes increasingly higher at a more rapid rate than 
does the percentage of infections, until finally in the class of 321 to 
360 years the two coincide. To be more explicit, the infections 
gradually begin to cause more and more measurable decay, until 
finally every infection has resulted in a cull case, no matter how slight. 
In the last two age classes both cull cases and infections have reached 
100 per cent; but again we are confronted by the small basis and this 
figure can not be accepted. There is no doubt that a tree by rare 
chance may escape infection throughout its life, but there is hardly 



36 



BULLETIN 871. U. S. DEPARTMENT OF AGRICULTURE. 



any possibility that when once infected sooner or later some cull 
will not result. 

To make the relation just discussed even more apparent the 
four sets of data have been plotted in figure 2. From this, it can 
be seen that the forrq. of the curves for severe cull cases and cull 
are the same, but differ quite markedly from the curve for infections. 
This shows clearly that infections alone are not the sole influence 
on the development of the dry-rot fungus, for if so the curves would 
have the same form. The slow progress of the dry-rot in the younger 
trees is very apparent. 

The curve for the cull cases is somewhat intermediate, at first 
inclining toward the severe cull cases and later coinciding with the 
infections. The younger trees are able to retard the fungus suffi- 







































































































iS^I 










5^ 


























4 




rfiV 






d* 


Up 


























y 


& 








/ ( 
































f 

















































































































































































60 
t; 50 

8 

30 
ZO 



O ZO 40 60 SO IO0 20 40 60 QO ZOO ZO 40 60 60 300 ZO 40 60 SO 400 

Age - years 
Fig. 2.— Relation of the age of incense cedar trees to infections, cull cases, severe cull cases, and cull. 

ciently to prevent many of the infections from developing into cull 
cases, but later this characteristic is obscured. 

The relative percentages of cull due to dry-rot on the various 
areas is not of importance from the standpoint of the present inves- 
tigation. That this will vary widely even within the optimum and 
intermediate ranges is self-evident to anyone who has been on 
logging operations where incense cedar is being cut. At times the 
variation, even in localities quite close to each other, is surprising. 
On the intermediate area the cull for all the trees amounted to 20.5 
per cent, while for the optimum area the figure was 16.8 per cent. 
These figures must not be taken as absolute, since it must be remem- 
bered that the areas were not clear cut. Practically every tree 
between the ages of 100 and 240 years was cut except those in which 
it was apparent that the age could not be accurately determined. 
Not all the trees below 100 years or over 240 years were cut, how- 
ever, since this would have meant an enormously increased cost 



DRY-ROT OF INCENSE CEDAR. 37 

without adding much to the investigation, the chief aim of which 
was to determine the age at which dry-rot became extensive and 
far-reaching. However, the relative representation of trees in the 
older age classes was maintained as far as possible, neglecting 
entirely, of course, the few very old veterans always found scat- 
tered through a virgin stand. 

The cull percentages given are indicative of the relative condi- 
tions that will exist in the intermediate and optimum ranges, 
although stands in the latter will on the whole be relatively more 
free from dry-rot than our figures indicate. However, the Office 
of Forest Pathology is now collecting figures for cull percentage 
bv a less intensive method over various localities, and these will 
include not only cull due to dry-rot but to all other causes as well. 

Before drawing final conclusions there is one other factor which 
must be considered in relation to dry-rot, namely, wounds or 
mechanical injuries. 

MECHANICAL INJURIES. 

The mechanical injuries which must be reckoned with are those 
caused by fire, frost, lightning, and the breaking off of branches 
as well as such miscellaneous factors as snow, falling trees, mammals, 
and wind. These injuries are important from three standpoints. 
First, they often afford an entrance to the heartwood of the tree for 
spores of wood-destroying fungi; next, the growth processes of a 
tree may be somewhat interfered with, resulting in a lessening of 
increment and a consequent tendency to suppression; and, last 
and least important, an actual loss in merchantable volume may 
result from the mere presence of the injury. 

Spores of the dry-rot fungus (Polyporus amarus) must have an 
entrance to the heartwood before they can germinate and develop. 
As long as the tree is protected by a layer of bark and sapwood it 
is immune from the ravages of dry-rot or any other heartwood 
destroyer. Small superficial wounds are quickly protected by 
resin exudation from the bark, which forms an antiseptic dressing 
on the wound, safeguarding it from fungous spores until the wound 
is finally healed or callused over. But incense cedar is poorly 
supplied with resin. Normally it is found in a limited quantity in 
the bark only, active in the inner bark, dry and hard in the outer 
bark. Large superficial wounds may often prove to be serious. 
If the bark is torn off over a large surface there is not enough resin 
available to form a dressing, the sapwood dries out and cracks into 
the heartwood, and these cracks offer an entrance for fungous spores. 
The most serious type of wounds, of course, are those extending 
deep into the heartwood, for then the heartwood is directly exposed 
to infection by wood-destroying fungi for the entire period of time 



38 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 

from the occurrence of the injury until it is completely healed over, 
and such injuries heal slowly. Wounds heal much more rapidly 
in young than in mature or overmature trees. 

The causes of wounds are taken up in the order of their importance. 



The most serious wounds, both numerically and in regard to 
the type of injury, result from fire. It is almost impossible to find 
a stand of timber anywhere in the Sierra Nevada or Coast Ranges 
which has not been visited by repeated fires. While the thick 
bark characteristic of incense cedar combined with the lack of 
resin in the wood makes it somewhat fire resistant, yet broad fire 
wounds commencing at ground level, reaching some distance up 
the trunk, and extending deeply into the heartwood are very fre- 
quent. These wounds are usually roughly triangular in shape, 
the base being at ground level and the apex at the top of the extent 
of the scar on the tree trunk. Considerable loss in merchantable 
timber results from the actual destruction of the wood, and there 
must be an appreciable decrease in increment until the tree read- 
justs itself to the loss in conducting tissue caused by the partial 
destruction of the sapwood and inner bark, which interferes with 
the conduction of water and soluble salts from the roots to the 
foliage and the return of elaborated food from the foliage to the 
roots. This loss is exceedingly difficult to gauge. Total loss in 
the merchantable timber occurs when a tree is completely girdled 
and killed or when the supporting tissue is so weakened by the 
wound that the tree is blown down. 

Large fire scars or "catfaces" are rarely caused by only one fire, 
but usually by successive fires, each one hollowing out the heartwood 
a little more. As many as 10 distinct fires have been found con- 
tributing to the formation of one catface. As long as the wood is 
completely covered by a charred surface the danger of inoculation by 
fungous spores is reduced to the minimum, but the wood dries out 
and checks, forming cracks extending into the unburned wood. In 
time, the charred surface is weathered away, and finally the heart- 
wood is exposed over the greater surface of the catface. Here is offered 
an excellent place for the entrance of a heartwood-destroying fungus. 

Wounded trees make strong efforts to callus over the injury, and 
this is often accomplished in course of time if the wound is not too 
large. Very large catfaces, particularly on mature or overmature 
trees, are rarely healed over. The prevalence of wounds caused by 
fire may be seen from Table VI. 

Table VI clearly show T s that fire injury was much more serious on 
the intermediate area than on the optimum area. The columns of 
greatest interest are the third and last. The third column (per- 



DRY-ROT OF INCENSE CEDAR. 



39 



centage with open fire scars) shows that of the total number of trees 
analyzed on the intermediate area, 38.3 per cent had open fire scars, 
while on the optimum area the percentage is only 23.5. In other 
words, these percentages of the total number of trees cut on the 
areas under consideration were still exposed to infection by wood- 
destroying fungi through fire scars alone. The last column indicates 
that 72.2 per cent of the trees on the intermediate area and 49.3 per 
cent of those on the optimum area have had open fire scars at some 
period of their life history, thus exposing them to inoculation by 
fungous spores. 

Table VI. — Incense-cedar trees found in the combined areas having fire scars. 





Number 
of trees 
(basis). 


Trees with fire scars (per cent). 


Locality. 


Open. 


Internal. 


Miscella- 
neous. 1 


Total. 




509 
566 


38. 3 
23.5 


33.2 
25.4 


0.8 

.4 


72.2 




49.3 








1,075 


30.5 


29.1 


• 5 


60.1 







1 Includes wounds probably but not certainly caused by fire. 

The internal scars on the intermediate area exceeded those on the 
optimum area by less than 8 per cent, but there were 15 per cent more 
open scars. This points to the fact that the intermediate area has 
been visited by more serious fires than the other, since, as has already 
L en pointed out, large catfaces are normally the result of repeated 
fires. 

The combined figures for all the areas show that a total of 30.5 
per cent of the trees had open fire scars, while 60 per cent suffered 
fire injury at some time. The column headed "Miscellaneous" in- 
cludes trees with scars not identified beyond all doubt as having been 
caused by fire. These are so few that they need not enter into the 
interpretation of the figures. 



Frost causes some injury in incense cedar but is not nearly as serious 
in this respect as fire. Frost cracks as a rule extend for some dis- 
tance up the tree and go deeply into the heartwood. A common place 
for the cracks to commence is just at the apex of an open fire scar, 
apparently a point of weakness in the tissues of the wood. Often 
they are somewhat spirally twisted around the trunk, distinctly 
reminding one of typical lightning scars. While frost cracks present 
only a very narrow opening for the entrance ol fungous spores, yet 
in length those cracks or clefts are often quite extensive. In many 
cases the wood around a frost crack is badly discolored, causing 
considerable loss in the merchantable contents of the tree. 



40 



BULLETIN" 871, U. S. DEPARTMENT OF AGRICULTURE. 



Typical frost cracks are rarely found except on large trees. Table 
VII shows the percentage of frost cracks on the trees analyzed. 

Table VII. — Incense-cedar trees found in the combined areas having frost cracks. 



Locality. 


Number 
of trees 
(basis). 


Trees with frost cracks 
(per cent). 




Open. 


Internal. 


Total. 




509 
566 


4.12 
1.41 


3.14 
.53 


7.26 




1.94 








1,075 


2.70 


1.77 


4.47 







Here again, as in the case of fire, the wounding is worse on the 
intermediate than on the optimum area. The percentage of trees 
exposed now or in the past to inoculation by fungous spores through 
the medium of frost cracks is rather low and not of great importance 
on any of the areas. Frost cracks in incense cedar are not nearly so 
prevalent as Meinecke (16, p. 31) found for white fir. 



LIGHTNING. 



Incense cedar suffers only slightly from injury by lightning. This 
is to be expected, since the dominant species in a stand and as such 
the taller trees (25, p. 36) are most subject to lightning stroke, while 
incense cedar rarely attains this position in the mixed stand in which 
it is found. Plummer (25, p. 33) also shows that incense-cedar wood 
is a poor conductor of electricity. 

An incense-cedar tree in the forest badly shattered by lightning 
is an exceedingly rare sight and immediately provokes comment. 
However, trees with slight lightning injuries are more common. 
Such injuries show as superficial wounds on the trunk. Often the 
wood is not scarred, but the bark and cambium are killed. The 
bark then drops away, exposing the sapwood, which in turn dries 
out and checks, offering fungous spores access to the heartwood. 
Long wounds extending spirally around the tree, so common in white 
and red fir in this region, are an unusual occurrence on incense cedar. 

Table VIII indicates the prevalence of lightning scars. 

Table VIII. — Incense-cedar trees found on the combined areas having lightning scars. 





Lo< ality. 


Number 
of trees 
(basis). 


Trees with lightning scars 
(per cent). 




Open. 


Internal . 


Total. 


Intermediate area 


509 
566 


1.76 
3.54 


2.53 
1.06 


4.31 
4.60 










1,075 


2.70 


1.77 


4.47 







DRY-ROT OF INCENSE CEDAR. 41 

Besides the trees shown in Table VIII, there were seven on the 
intermediate area and five on the optimum area with slight wounds 
which appeared to have resulted from lightning; but an absolute 
determination was impossible. The meager basis in this table shows 
practically an equal number of lightning-scarred trees in the two 
localities. 

BREAKING BRANCHES. 

Incense cedar does not prune itself easily even when growing in a 
dense stand, a fact attested by the persistence of the lower limbs. 
In time, however, some of the lower branches die and break off. The 
dead stubs then offer a point of entrance for heartwood-destroying 
fungi : the spores lodging in the dead wood may germinate, develop, 
and the fungous hyphae pass through the bark and sapwood of the 
tree into the heartwood by way of the pin knot. The pin knot in 
this case plays exactly the same role as an open wound, but it must 
be remembered that the area for lodgment of a fungous spore on a 
pin knot that is not healed over is exceedingly small in comparison 
with other types of wounds. On the other hand, there are normally 
from several to many open pin knots on each tree, and every tree, 
throughout all but the earliest years of its life, is thus exposed to 
inoculation by fungous spores through these open pin knots. Many 
of course heal over, but others take their places. 

OTHER CAUSES. 

Besides the causes of wounds already discussed, there are a few 
others of minor importance. 

Strong winds will occasionally break off branches or tops, or over- 
throw entire trees, particularly those weakened by a bad open fire 
scar in the butt. The thick foliage of incense cedar collects a very 
heavy weight of wet snow, often causing the tops and branches of 
young trees especially to break off. Sometimes a falling tree will 
rake off the limbs and part of the bark of a neighbor. Such injuries 
are usually superficial unless very large branches have been broken 
off or the bark has been torn away from the trunk over a considerable 
area. 

Man is at times directly responsible for certain wounds. It is quite 
a common sight along a newly constructed road to see bark torn off, 
often rather high on the trunk, where the tree has been struck by a 
flying rock from a powder blast. Some wounds result from blazing 
trees to mark a boundary line or trail, but they are usually small and 
rapidly heal over. 

Broken or dead tops, the cause of which is often impossible to 
determine, are not at all rare. Trees with these injuries comprised 
6.9 per cent of the total number on the intermediate area and 7.1 
per cent on the optimum area. 



42 



BULLETIN 871, IT. S. DEPARTMENT OF AGRICULTURE. 



PREVALENCE OF INJURIES. 



Most incense cedars do not attain any great age or size without 
suffering some injury. Many old trees, and more rarely young ones, 
show numerous injuries, often fire, frost, and lightning having com- 
bined in the wounding of a single tree. Of the 509 trees on the 
intermediate area only 116, or 22.8 per cent, escaped without injury, 
while on the optimum area 38.9 per cent, or 220 of the total 566, were 
free from wounds. This difference is explained by the fact that the 
risk from injury has been greater on the intermediate area than on 
the optimum area, while a greater number of young trees were cut 
on the last-named area than on the first. The risk of injury is 
cumulative, increasing with the age of the tree. 

This cumulative risk of wounding is shown clearly in Table IX, 
in which the trees from all areas are combined and arranged by 40- 
year age classes. Only those trees the ages of which it was possible 
to determine exactly are included in this table, while the data on 
wounds previously presented include all the trees. This accounts 
for the apparent slight discrepancy between the figures on the total 
number of trees involved. 

Table IX. — Incense-cedar trees showing cumulative wounding in the combined areas. 



Age class. 


Number 

of trees 
(basis). 


Total 
with 
wounds 
(per 
cent). 


Trees 
with 
severe 
wounds 
(percent- 
age of 
total 
wounds). 


Age class. 


Number 
of trees 
(basis). 


Total 

with 

wounds 

(per 

cent). 


Trees 
with 
severe 
wounds 
(percent- 
age of 
total 
wounds). 


1 


a 


3 


4 


1 


2 


3 4 




1 

51 
185 
284 
233 
118 

94 



29.4 
48. 6 
59.2 
74.3 
82.2 
92.6 




6.7 
14.4 
28.6 
35. 2 
44.4 
43.6 


281 to 320 years , 
321 to 360 years 
361 to 400 years 
401 to 440 years 

Combined 


49 
19 
4 
2 


98 
100 
100 
100 


62.5 




68.5 


81 to 120 years 

121 to 160 years 

161 to 200 years 

201 to 240 years 

241 to 280 years 


100 
50 


1,040 


67.6 


36.3 



In considering the figures in Table IX the reader should keep in 
mind the fact that since branch stubs are not treated as wounds, 
wounded trees practically mean fire-scarred trees, as the number of 
wounds from causes other than fire have been shown to be insig- 
nificant. 

Considering column 3, which expresses the ratio of the wounded 
trees to the total trees, it is seen that the trees are subject to con- 
siderable wounding at a very early age and that this percentage 
increases very rapidly, until in the older age classes every tree has 
been wounded and consequently at some time exposed to infection. 



DRY-ROT OF INCENSE CEDAR. 



43 



Not only does the total number of wounds increase with age in a 
stand, but the number of severe wounds becomes proportionately 
greater. Each tree was given a wound rating (x), x, xx, or xxx, the 
first symbol indicating very slight wounding and the last very 
severe. In Table IX trees with a rating of xx or xxx are con- 
sidered as severely wounded. In all cases the character as well 
as the extent of the wounding and its relation to inoculation by 
spores of the dry-rot fungus was carefully taken into account in 
applying the rating. 

In column 4 of Table IX it is seen that while in the age class of 
41 to 80 years only 6.7 per cent of the wounded trees are severely 
wounded, an almost steady increase brings this figure to 68.5 per 
cent in the class of 321 to 360 years. This is to be expected, espe- 
cially since fire scars predominate, because large scars of this type 
are almost invariably the result of recurring fires, and in the past 
virgin stands in California have been fire swept time and again. 
The two oldest age classes can not be given much weight, owing to 
an insignificant basis. 

The above figures demonstrate the rather slight chance an incense 
cedar has of rounding out its life without a reduction in its normal 
increment through an injury interfering with the growth processes 
or a reduction in its actual content of merchantable timber, either 
directly from a wound or by a wound affording an entrance for a 
heartwood-destroying fungus, in this instance most probably the 
dry-rot fungus (Polyporus amarus) . 

RELATION OF DRY-ROT TO MECHANICAL INJURIES. 

The intimate connection of various kinds of wounding, especially 
fire, with infection by the dry-rot are shown in Table X. The 
infections are grouped under their respective causes and percentages 
for each cause, figured on the basis of the total number of infections. 
Trees of uncertain ages are included in these figures, since it makes 
no difference in this table whether or not the absolute age of the 
tree is known. 



Table X. — Mode of entrance of dry-rot infections of incense-cedar trees. 





Number 
of infec- 
tions 
(basis). 


Means of entrance of infections (per cent). 


Locality. 


Fire 

scars. 


Knots. 


Wounds, 
cause 
un- 
known. 


Light- 
ning 
scars. 


Un- 
known 
causes. 


Frost 
cracks. 


Broken 

or dead 

tops. 


Intermediate area 


322 
334 


75.8 
58.7 


19.3 
31.1 


0.6 
5.1 


2.5 
1.5 


0.9 
2.4 


0.6 
.9 


0.3 


Optimum area 


.3 






Combined 


656 


67.1 


25.3 


2.9 


2.0 


1.7 


.8 


.3 







44 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 

Table X shows that on the intermediate area nearly 76 per cent 
of all the infections entered through fire wounds; this means of 
entrance for the optimum area is approximately 59 per cent, while 
for all the areas combined it is almost 70 per cent. Since fire scars 
are almost invariably found in the base of the tree, commencing at 
ground level, these figures are at variance with Von Schrenk's (26, 
p. 69) idea that "the decay begins somewhere in the upper part of a 
tree." 

Besides fire wounds being responsible for such a high percentage 
of the infections, inoculations through wounds of this character 
quite commonly lead to very serious and damaging dry-rot, even 
in some of the younger trees. In many cases, even in old trees, a 
long continuous pocket of dry-rot, sometimes having a linear extent 
of 10 feet, will follow a healed fire scar, running out at the end of 
the wound, with no further decay extending up the tree. Such 
infections do not appear especially serious, but it must be remembered 
that the most valuable portion of the trees, the heartwood in the 
butt log, is damaged. On the other hand, the fungus evidently 
finds conditions highly unsuitable in the wood back of a large open 
fire scar. Almost every tree with this type of wound appeared 
sound on the stump when felled, but serious dry-rot appeared at 
the first cut above the open fire scar. When such logs were split, 
it was found that the pockets of dry-rot commenced just at or a 
little above the top of the open fire scar, but rarely lower down. 
The avoidance of the dried-out wood around an open fire scar by 
the mycelium of this fungus is not at all in keeping with the results 
of experiments of Munch (19, 20, 21), which emphasized the highly 
favorable influence of an increase in oxygen coupled with a decrease 
in moisture in the host tissues on the development of various wood- 
inhabiting fungi. There should certainly be a big increase in the 
oxygen content of heartwood directly exposed to the air over that 
protected by a heavy layer of bark and sapwood, thus, according to 
Miinch's theory, causing very serious dry-rot in the wood around 
open fire scars. The exact reverse of this is the condition actually 
existing. However, every wood-inhabiting fungus must have cer- 
tain minimum physical requirements for its growth and development. 
Possibly the dried-out wood in this case falls below the minimum 
water requirement of Polyporus amarus, or it may be that certain 
chemical changes in the wood brought about by more or less ex- 
posure to the air inhibit the growth of the fungus mycelium. 

Not every fire scar is inoculated, but the chances for inoculation 
with subsequent infection are rather high, owing to the relatively 
large area of heartwood exposed offering a broad surface for the 
lodgment of spores of the dry-rot fungus. On the optimum area, 
70 per cent of the trees wounded by fire subsequently became infected, 



DRY-ROT OP INCENSE CEDAR. 45 

on the intermediate area 64 per cent, and on the combined areas 67 
per cent. The percentage of risk of a tree with a fire scar becoming 
infected is very high. 

Next in importance to fire scars as a means of entrance for dry- 
rot come knots. Of the infections on the intermediate area 19 per 
cent entered in this way and 31 per cent on the optimum area, while 
for the areas combined the figure is 25 per cent, a little more than 
one-third as many as were traced to fire scars. The greater part of 
such infections, because they rarely extend beyond the wood of the 
knot itself, are of little or no importance as compared with fire scars 
in promoting serious cull. Of the total infections entering through 
knots only 48 per cent resulted in cull cases and 12 per cent in severe 
cull cases, while in infections through fire scars, 80 per cent of the 
total became cull cases and 38 per cent severe cull cases. The above 
data were at first tabulated by 40-year age classes, but this brought 
out nothing of importance. In the case of infections through fire 
scars most of them developed into cull cases in every age class; 
while for infections through knots up to 200 years less than half 
developed into cull cases, but beyond that age the cull cases became 
more numerous. 

Considering all the severe cull cases as 100 per cent, it is found 
that fire is responsible for 84 per cent, knots for 10 per cent, and all 
other causes for the remaining 6 per cent. Furthermore, 81 per 
cent of the total volume of cull caused by dry-rot resulted from 
infections entering through fire scars. This demonstrates the 
serious r61e played by fire in connection with dry-rot. Fire scars 
are responsible for by far the greater number of infections, and a 
high percentage of these infections results in severe cull cases. 

Knots are of some importance, though, in promoting severe cull 
cases throughout the life of the trees, even in the younger age classes. 
For example, of the fourteen severe cull cases occurring in all the 
trees up to 165 years of age, four entered through knots. 

Of course, every tree is exposed to infection in this way throughout 
all except the very earliest years of its life, not only at one but at 
several points, since each tree usually has from several to many open 
knots or branch stubs, whose dead wood offers a bridge for the 
fungus from the outside through the bark and living sapwood into 
the heartwood. However, each knot presents only a very small 
surface for the lodgment of spores of heartwood-destroying fungi. 
Out of the total number of trees open to inoculation through knots 
on the optimum area only 18.2 per cent became infected in this way, 
on the intermediate area only 11.4 per cent, and for all combined 
just 15 per cent. In other words, in the trees studied the chances 
for a tree becoming infected with dry-rot through branch stubs were 
merely 15 out of 100. 



48 



BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 



order to emphasize the fact that while the increase in the number of 
wounds is closely followed by an increase in infections, the increase 
in the amount of cull due to decay is not a direct function of the 
increase in infections, but is also dependent upon the factor of age 
and thrift, as previously explained. 

Meinecke (16, pp. 47-48) found in white fir that a combination of 
suppression and severe wounding was a prerequisite for serious 
decay in trees up to the age of 150 years. This does not hold for 
incense cedar. Of the ten severe cull cases in suppressed trees up 
to the age of 165 years, five occurred in trees slightly wounded, one 
in an entirely unwounded individual, and only four on severely 
wounded trees. Of the four dominant trees below the same age 
with severe cull cases, two are severely wounded and two slightly 



| 40 



































































































v^ 


*&> 


(JCV 




































' \f\ 






















































































A/ 






































t 


Y 









































































































































O 20 40 60 60 100 20 40 60 SO- ZOO ZO 40 60 60 300 SO 40 <SO 00 400 

Age - Years 
Fig. 3.— Relation of the age of incense-cedar trees to wounds, infections, and cull. 

wounded. And, in fact, throughout all the age classes occur trees 
slightly wounded but with severe cull cases. 

The foregoing considerations lead to the following conclusions: 
(1) Fire is responsible for by far the greatest number of dry-rot 
infections, commonly leading to serious decay, resulting in heavy 
cull. Fire is three times as important as its closest competitor, 
knots. (2) Knots are responsible for some far-reaching decay, but 
most of the infections through knots are confined to the immediate 
vicinity of the knot. (3) Aside from fire and knots all other means 
of entrance for decay are of little import. Lightning would be 
serious except that wounding from this source is rare. Frost is of 
no importance in promoting inoculation, since the wounded surface 
presented is small and frost cracks are relatively few. However, 
frost cracks often assist in carrying the dry-rot over a greater length 
of the bole than would be normal. Damage from unknown causes 
leads to some infection, but it is not of much importance. Infections 



DRY-ROT OF INCENSE CEDAR. 49 

through dead or broken tops are so insignificant that they may be 
entirely disregarded. (4) Severe wounding is not a prerequisite for 
severe cull cases or extensive decay at any stage in the life of incense 
cedar. 

APPLICATION OF RESULTS. 

RELATIVE IMPORTANCE OF DRY-ROT. 

In the foregoing discussion the one big factor which stands out 
almost to the exclusion of all others is the dry-rot. Mechanical 
injuries of certain types play some r61e, not only in destroying 
merchantable timber values but in lessening the annual increment. 
However, it is chiefly the fact that wounds are the means for the 
entrance of dry-rot which makes them of any but insignificant 
importance. 

Factors reducing the annual increment of the host, namel} 7 , Oym- 
nosporangium blasdaleanum, Phoradendron juniperinum libocedri, Stig- 
matea sequoiae, and Herpotrichia nigra are of minor importance. In 
fact, only the first two named, being decidedly ubiquitous, are 
worthy of the least consideration; but the resulting loss is so slight 
and intangible that under present conditions it may well be disre- 
garded except incidentally. The rare trifling loss in merchantable 
timber from burls of the mistletoe can not be of consequence. 

Fungi such as Polystictus abietinus, P. versicolor, Polyporus volva- 
tus, and others (see p. 4), only attacking dead wood and never 
found on living trees, are to be regarded as beneficial, since they 
hasten the decomposition of ground litter, thus increasing the humus 
in the soil and removing a serious fire menace. 

Loss resulting in the heartwood of living trees from the so-called 
secondary rots is very slight in the aggregate. It is rare that such 
decays are at all far-reaching, and, furthermore, it is possible that 
certain of them may be abnormal forms of the dry-rot. 

To repeat, then, the one big consideration from a pathological 
viewpoint which must hold above all in the silvicultural treatment 
and utilization of incense cedar is the dry-rot, together with the 
interrelated mechanical injuries. 

CONTROL OF DRY-ROT. 

Very little can be hoped for in the line of any serious consideration 
or attempt at direct control of dry-rot on private holdings for years 
to come. The private owner is averse to any increase in expenditures 
which does not show prospects of immediate gain. On certain private 
holdings where the incense cedar was heavily affected by dry-rot, all 
the trees have been left standing, only the more valuable species 
being removed, leaving the diseased individuals to continue spreading 
the decay to uninfected members of the present and future genera- 
tions. 



52 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 

particularly likely to be followed on double-length logs (20, 24, 28 
feet, etc.). But invariably the dry-rot will commence just at the 
top of the fire scar and almost immediately spreads out over the 
entire radius of the heartwood. In other words, in a log with an 
open fire scar showing on the base but otherwise sound and with 
pockets of dry-rot in the top end, the decay should be considered as 
beginning at about the top of the fire scar and extending from there 
to the upper end of the log in practically the same degree and radial 
extent with relation to the heartwood as is shown on the top end. 

Advance rot (see p. 13) should be treated just the same as mature 
dry-rot. 

In the case of a large swelling on the bole caused by mistletoe it 
is best to have the tree bucked in such a manner as to exclude t\ie 
swelling rather than have such a defect reach the landing as part 
of an otherwise sound log and then be scaled out. 

MARKING. 

Timber sales at present offer the only extensive means of prac- 
ticing intensive silviculture on our National Forests, and the entire 
results are absolutely based on correct marking. Fundamentally, 
the object of marking is to leave the stand in the optimum condition 
for its future welfare and development. This goal should never be 
lost sight of, no matter how clouded the issue may be by a com- 
plexity of immediate and often pressing considerations. To attain 
this end requires a high degree of skill, grounded on a thorough 
understanding of all the factors involved, not the least of which are 
those making for total loss in the species under consideration. 

The fundamental object of marking has been far from completely 
attained if, after cutting, diseased individuals are left standing to 
carry infection to otherwise sound trees of merchantable size, besides 
menacing the future of the advance growth and reproduction. 
Obviously, then, trees with sporophores or shot-hole cups should 
invariably be marked for cutting, for these are positive proofs of 
damaging dry-rot. Such trees are as a rule not only a total loss, 
being unmerchantable from the butt to varying distances of 10 to 
50 feet above the highest sporophore or shot-hole cup, but are the 
most potent factors in spreading infection to other trees, since infec- 
tion can only be brought about by spores coming from sporophores 
on diseased trees. True enough, shot-hole cups in themselves do 
not menace surrounding trees with possible infection, but they do 
indicate that the fungus has reached fruiting maturity and is very 
likely to develop more sporophores, as is attested by the not un- 
common occurrence of two or more shot-hole cups of varying ages 
on the same tree. Furthermore, the fungus mycelium in any in- 



DRY-ROT OF INCENSE CEDAR. 53 

fected tree possesses the potential capacity of sooner or later pro- 
ducing sporophores. 

Remembering the great percentage of dry-rot infections entering 
through wounds, trees with injuries must be treated accordingly. 
Trees with healed wounds are of less concern than those with open 
wounds, since the former, if not already infected, are immune except 
for the inevitable, though fortunately not frequent, attack through 
branch stubs, while the lattei are still open to infection. Then, too, 
the area of heartwood exposed by the injury is of grave consequence; 
the larger the area the greater the opportunity for infection. We 
already know the high percentage of infections through fire scars 
which so commonly expose large areas of heartwood; therefore 
fire-scarred trees, above all, should be marked as heavily as possible. 
Large lightning wounds are a serious danger, but small superficial 
injuries, especially if high up on the bole, can be almost disregarded. 
Frost cracks, though by virtue of the exceedingly small amount of 
heartwood they expose offering slight chance for infection, often 
aid in spreading infection established through some other agency, 
and trees with such wounds should be marked for cutting whenever 
possible. From the pathological viewpoint spiketops or stagheads 
may be almost disregarded except for their suppressing influence 
on the injured individual, but sound silviculture demands the re- 
moval of such trees from the stand. 

Even if the Utopian dream of a forest community without injured 
individuals could be attained, this in itself would not result in com- 
pletely controlling the destruction wrought by the dry-rot fungus, but 
only in minimizing it in a great measure. There would still be some 
loss from infections entering through knots. Then, too, no matter to 
what degree of intensive management a forest in this region may be 
brought in the future, some injuries will always occur, even from fire, 
while frost and lightning wounds are inevitable. The unavoidable 
injuries to a certain number of the seed trees during logging on any 
yales area must not be overlooked. 

Therefore, all wounded trees must not only be eliminated on sales 
areas, but trees, even though unwounded and thrifty, must not be 
left with the expectation that they will be sound at the next cutting 
if by the time the cutting takes place they will have attained or 
passed beyond the age at which loss from dry-rot becomes of serious 
economic importance. It has been shown that the critical age occurs 
at 165 years and the age of decline at 210 years. Beyond the age of 
165 years suppressed trees become subject to extensive decay, while 
up to that age they may be expected, with rare exceptions, to remain 
relatively sound, the same being true for the dominant trees at an 
age of 210 years. 



54 BULLETIN 8*71, U. S. DEPARTMENT OF AGRICULTURE. 

Since in the intermediate range all but an insignificant percentage 
of the trees are suppressed in a greater or less degree, it becomes 
obvious that in this region incense cedar should be cut by the time 
it reaches 165 years, the critical age. 

In the optimum range, suppressed trees must not be allowed to 
pass 165 years and dominant individuals 210 years (the age of decline) 
before felling. 

Even in the distant future, when the risk of wounding in the 
forests is reduced to a minimum, it is highly problematical whether 
a new age of decline can be established at a higher age, on account of 
the entrance of decay through knots. Damaging dry-rot has entered 
trees through knots beginning at 105 years, and while such cases are 
rare in the years below the critical age and age of decline, yet they 
are sufficient to indicate that this condition will always have to be 
reckoned with. Furthermore, as time goes on, the increasing value 
of timber will result in noticeably lowering figures as to what con- 
stitutes an allowable percentage of cull in any species. 

From a pathological viewpoint the critical age must limit the rota- 
tion of incense cedar in the intermediate range. It is doubtful 
whether even in the managed stands of the future the incense cedars 
in this range will be other than suppressed in most cases, since the 
present widespread suppression does not seem to be the result of any 
influence that could be removed by a system of forest management, 
arising apparently from the fact that the cedar is removed from the 
region of its optimum development. 

In the optimum range the rotation must be limited by the age of 
decline. The critical age is not so important except during the period 
of transition, for suppressed trees, while common enough in the virgin 
stands of to-day in this range, will have little place in the managed 
stands of the future. Here, the species being in its optimum, nothing 
but thrifty, dominant individuals should be produced under a rational 
system of management. 

The influence of decay on harvesting a timber crop was hinted at 
years ago by Von Schrenk (27, p. 203) and clearly pointed out by 
Meinecke (16, p. 61) for white fir. Mitchell (17, p. 32) took this 
so-called pathological rotation carefully into account, recommending 
a rotation of 150 years, at which time the species attains a good 
merchantable size. The rotation recommended by Mitchell is based 
on Meinecke's preliminary study of dry-rot. 

As a result of the present study, the pathological rotation for 
incense cedar must be placed at 165 years in the intermediate and 
210 years in the optimum range. During the transition period, while 
suppressed trees are still a factor in the optimum range, these should 
be cut when not older than 165 years. This does not mean that in 
the two regions under consideration cedar can best be cut at regular 



DRY-HOT OF INCENSE CEDAE. 55 

intervals of 165 and 210 years, respectively, but simply that if it is 
left to a greater age there is a full realization of the resulting enor- 
mously increased loss through dry-rot. The pathological rotation 
becomes a maximum limiting factor for the actual rotation, which 
may be financial, silvicultural, or one of maximum volume, depending 
on conditions in the future. From present indications it is highly 
probable that all other rotations for incense cedar will fall below the 
pathological rotation in both regions; the difference will be quite 
marked in the optimum range. It is possible in the optimum range 
that during the transition period, if necessary to leave suppressed 
trees standing after cutting, the increased vigor of such individuals 
which may follow the opening up of the stand might raise the critical 
age somewhat, but in the present state of our knowledge not only 
regarding the influence of thinning on the development of wood- 
destroying fungi in standing trees, but in the case of incense cedar 
regarding the actual response of the trees themselves, this consider- 
ation is entirely too hypothetical to influence our present conclusions. 

SUMMARY. 

The results of this study point to the following main conclusions : 

(1) Incense cedar is classed as an inferior species because of a 
uniformly heavy percentage of cull caused by the dry-rot fungus 
(Polyporus a?narus). Judicious scaling and instruction in the proper 
methods of bucking will ultimately aid materially in changing this 
view. 

(2) Dry-rot can be eliminated in a large measure from future stands 
by intensive fire protection, but it can not be entirely controlled in 
this way, owing to the continued occurrence of unavoidable mechan- 
ical injuries caused by pruning, lightning, and frost. 

(3) The following directions should apply to marking on timber 
sales : 

(a) Trees with sporophores and shot-hole cups must be marked for cutting. 
(6) Seriously wounded trees, especially those with fire scars, should be marked to 
be cut. 

(c) In the intermediate range all but a very small percentage of the trees are sup- 
pressed. Since suppressed trees are subject to severe dry-rot after they pass the 
critical age of 165 years, trees left standing should be of such an age that they will not 
pass that age before the next cutting occurs. Dominant trees, being so few, may be 
classed with suppressed trees, but in reserving seed trees only the most thrifty indi- 
viduals should be considered. By this practice some dominants will be among the 
trees left, and these will be safe until the age of 210 years is reached. 

(d) In the optimum range, suppressed trees are subject to damaging dry-rot after they 
pass the age of 165 years (the critical age), while dominant trees are safe until 210 years 
(the age of decline) is reached. Therefore, suppressed trees left standing must be of 
such an age that they will not pass the critical age (165 years) before the next cutting 
occurs, and dominant trees left should not pass the age of decline (210 years) before the 
next cutting. Suppressed trees, however, should be heavily marked for cutting and 
only left unmarked if unavoidable. 



56 BULLETIN 8*71, U. S. DEPARTMENT OF AGRICULTURE. 

(4) The rotation for incense cedar must not exceed 165 years in 
the intermediate and 210 years in the optimum range. 

If for any reason the pathological rotations, as determined in this 
paper, must be exceeded in future operations on cut-over lands, 
the forester in making the decision will have a full realization of the 
enormous loss in merchantable timber to be faced through cumulative 
risk of cull due to dry-rot in the stands so handled. 



DRY-ROT OF INCENSE CEDAR. 57 

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1913. Logging . . . ed. 1, 590 p., 132 fig. New York, London. 

(2) Chapman, H. H. 

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58 BULLETIN 871, TJ. S. DEPARTMENT OF AGRICULTURE. 

(18) Moller, A. 

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